We're starting with 5th level characters and a player is making a Ranger with the Beast Master Archetype and would like to select a Psuedodragon for the companion even though it's not considered a "Beast" within the rules.
We're using Starting Equipment "Standard Campaign" rules out of the DMG on page 38. The character has of 725 gp in starting money and has purchased wagon and horse and enough supplies to brew beer and ale so they have close to 600 gp left over.
In general I don't disallow giving a player what they want, though it might be at a cost.
Is setting a gp cost for the character aquiring a Pseudodragon a reasonable cost, if so how much would be reasonble?
Limiting the telepethathy to be only between the character and the pseudodragon might be reasonable hindrance as well? This is something we can always change in the future if the pseudodragon and the character adventure for a long period of time.
I would also might give the pseudodragon a kind of mishievious personality just to make things fun.
I'm curious what other DM's might do in this case.
It's probably fine to use a pseudodragon for a beast master ranger's companion at no cost to the character and no change to the monster. Do work with the player to give it an interesting personality and goals of its own - but let the player control it.
Slight difference of opinion here: it is an intelligent creature so I wouldn't let the player outright control it. The player can try but the DM should be the arbiter as to whether the pseudragon does the particular action. Totally depends on the player, though.
Give it some of the traits and what-not from the "personality & backgrounds" section. Have the player roll the dice and see what they get, maybe it'll be a miscreant. 