Level is easy, progression isn't
Pseudodragon has 2 racial HD, +3 level adjustment and 1 level of sorcerer which makes for a 6th level PC.
With so many abilities, working out a 5-level progression for the little fella is not going to be easy but here are some suggestions:
HD: 2 - 1 at first, 1 at third
Ability bonuses: -4 str, +4 dex, +2 con, +2 wis - start with -4 str, +4 Dex, add +2 con at 2nd and +2 wis at 5th
Special attacks: Poison at 1st-3rd level, +2 racial bonus to DC at 4th-5th
Special qualities: Blindsense 60 ft., darkvision 60 ft., immunity to sleep and paralysis, low-light vision, spell resistance 19, telepathy 60 ft - sheesh, start blindsense at 20ft and add 10 ft per level, start with full darkvision and low-light, give immunity to sleep at 1st-3rd and immunity to paralysis at 4th-5th, spell resistance 5 at 2nd, 10 at 3rd, 15 at 4th, 19 at 5th. Telepathy at 5th.
Also need to think about racial bonuses to hide (+4/+8) and fly speed (start at 30' and increase to 60' by level 5
Saves: All good; +2 at first, +3 at 3rd
AC: +4 natural - start with 0, add one at each level
Put all the above into a table and massage for balance.
Bigwilly