So, our first play session was.... interesting. My 4 players plus my DMPC made for 5 characters. One of them decided to split off to get some info from the cultists during the raid and never rejoined the main group. He made it to the keep. My character got killed trying to front line and protect the other PCs. That fight chewed them up pretty good so they sought shelter in an already looted home for a short rest. When they set out to finish getting to the keep, the last group dropped all of the remaining PCs. Only one made his death saves and regained an HP three hours later. Once he came to, he bolted out of Greenest and stopped in Berdusk. Each group of enemies being 2 to 10 was intense. It also didn't help my players put an additional encounter on themselves by sniping out a group as they approached the city.
That's the situation. I'm left being fairly WTF as a DM. The raid has continued on the town for at LEAST 3 hours and the implication of that remains. Now, I need to figure out how to get the guy in the keep back with the guy who ran in addition to introducing the new characters. The guy in Berdusk is fairly easy but has a stated goal of going further away from Greenest. Which I'm using that city to introduct the new characters and likely will try to use the Harpers there to turn him around. Throwing in some extra fights and investigatory stuff on the way back should get them back up to proper XP. I'm still left with what to do with the guy in the keep. He's going to see some things but have none of the requests to go out on his own. I can't see the Governor making that request of a single dude. I also can't see him sitting tight once the raid stops and the coast is clear. That gives him probably at least a day to himself that I need to play through with him.
Any critiques on my plans going forward? Tips? I am new to running a FR campaign, but I have the 3.0 setting book. Hell, I'd enjoy just hearing your first session story to Hoard. Thanks!
Nothing? Lol
Why not have a new PC join the loner in the Keep? Then make it their first mission to rescue the rest of the gang!
-Vargtass
If the encounters are too much try this...a bit radical but I did this in 4E once and it worked well.
Berdusk thinks that they are next, so they mobilize their militia to INVADE Greenest to kick the Cult out. Each character gets to lead his/her own battalian. It becomes a combat/non-combat encounter with making Charisma checks to have your PCs rally the troops and see how the fight is going. Anyone who wants an actual encounter can fight a group of opponents tehmselves that they can handle ie: 2 kobolds. If that PC wins the fight, their next Charisma check gains advantage. You need X number of successes before Y number of fails to get to the keep. Once at the keep, the PCs can hook up with the guys who is in the keep who can use his time to find the tunnel and heal up. If that's too much time, then maybe a mole inside the keep saw him as a threat and knocked him out with poison and he wakes up a few days later after some townsfolk keep him stable.
In my opinion, I think you now have an excellent foundation to build upon. Each of your players now understands the full threat of the Cult of the Dragon and probably feels more than a little pissed off that they almost got TPK'd. At this point, I would suggest that your players reroll new characters and then you should find a way to introduce them back into the story. Personally, I would have them reroll as members of the city guard who could be then given the missions by the Governor. You could continue to hammer the point home that the Cult is no joke by starting them with the dragon encounter. For the longer term, I could see the character who bolted rejoin the party once they get to the point where they are escorting the Cult's treasure to try and determine where it is heading.
As I said at the start, your foundation is brilliant. Don't apologize for it. Use it and move forward.
Alternately, have the characters awaken in the dragon nursery from Chapter 3. They're being used to feed the dragon hatchlings. Have them fight their way out of the nursery, recover their arms and armor, and escape the camp. After that, they'll be level 2 or 3, a bit more resilient and/or cautious, and have a grudge against the Cult.
Is Hoard designed for players to start at level 1? where should they be by the end?
It seems to me that a party which attempts to brute force their way through the village in order to reach the keep is going about things in the most difficult way possible. With all of the motley groups participating in the raid, it shouldn't be all that difficult for the characters to bluff their way past a lot of encounters. A character with the Friends cantrip, the Charm Person spell, or the Disguise Self spell might even be able to arrange for an armed escort to the keep if they go about things cleverly. I guess my point here is that experienced players should pretty quickly recognize that they are in over their heads, and if the players are inexperienced, then you might consider using your DMPC in order to nudge them in the right direction next time. This does not really answer any of your questions, but your account of the adventure serves as a pretty good cautionary tale for other groups who are attempting this part of Hoard of the Dragon Queen. The adventure was pretty clearly written before the monster math was fully nailed down, so a party of level 1 adventurers is in over their heads unless they are both lucky and clever.
Thanks everyone! I wasn't expecting that kind of response after crickets.
Thankfully, the guy who got trapped in the keep (rogue) went north to Berdusk as well. This started out as a solo session to just resolve his actions but exploded into a full on, nothing but roleplay session including the introduction of my new DMPC (sorcerer) and a relation to one of the humans that died - his brother, actually, (druid) as that family was from Berdusk. So, he got a front row seat to the rest of what happened that night and rested up, stole a horse, and fleed town. He went to Berdusk disguised as his former companion not knowing that was where he was from and ran squarely into his brother practically right after he just got informed about his brother's death from the guy who got there earlier (a bard).
The bard was bitter at the rogue for running off and tried to basically said he was a member of the cult of the dragon. The brother druid tried to petition Lady Cylyria to jail the rogue for shenanigans based on what the bard told him who then gave him a writ acknowledging his grievance against the cult and ordered an expetionary force to be sent to Greenest. The bard actually got picked up by the guard and questioned but was detained in the city for a couple days as they tried to track down the rogue. The rogue, however, has the dual identity thing going on so they never spotted him. In the mean time, the bard and all of the characters orchestrated a public charity benefit for Greenest. I ended the session as there was one more character introduction that needed to happen before they set out but things ended with them buying a wagon and mule plus provisions for Greenest. I gave them some roleplay xp and overall it appeared everyone had a good time.
I agree the raid on Greenest is intense if you try to brute force it which is what they did. It feels like I'm having to disabuse my group from the idea that "combat = progress." Thankfully, since they haven't inflitrated the camp, they can still do that and events can presume as previously planned. However, with this group things rarely go as planned. 
The one who fell...
A hobo finds the body and drags it into the sewers and prepares to devour it... right in front of the doorway to the tunnel that leads into the keep... right as the heroes enter to take cultist captives. The one who ran... let him hole up with the people in the temple and be rescued in that encounter and healed by the cleric in the temple... or tied up in the mill, bound and hung on a rope being slowly lowered into the grinding wheel of the mill... as the heroes enter. Plenty of ideas. Think how they would do it in pulp tales.
Garrett