Why warlock/wizard?
Would sorcerer be better since both are charisma based?
As for my own char:
For a level 20char I would have taken lore bard 18/hexblade2.
A skill monky who can heal, buff, debuff and with the right selection of non bard spells even damage.
As written above criminal or urchin background for thief tools, so I can also work as rogue.
Hexblade gives be some profiencies, the most damaging cantrip and I can use cha for 1h weapons.
For a lv 10 char I am not sure if 1 (or even 2) lv warlock is worth losing bard 10.
The bard could select 2 more spells from another class and become expert in more skills.
Bard is especially good for me, I can finally overcome my hatred for bards that I had since BG1, were the bard was my most useless party member.
Edit: I deleted some stuff were I was wrong.
All casters benefit from 3 levels of Sorcerer. Metamagic is extremely strong.
Bards are very strong in BG and SOD because they can most benefit from spell scalling since they level faster than any class. They kinda lose utility in BG2 because you can get to lvl 40 (31 with casters), and therefore Bards advantage wears off.
In 5e they are probably the best caster. They can do everything, cast everything, buff, heal and still have utility.
