I never use pick pocket, I read that it doesnt max out at 100 points, some NPCs need several hundred pick pocket points to successfully pick.
As for picking locks, The knock spell works on all pickable locks in BG2 so open locks isnt too important. Also in BG2, you get two rings that give +25 to open locks and disarm traps.
Trap skill is the only important one to get to 100, open locks can be left at around 75, and I usually dump the rest into set traps and stealth.
With a dual Thief / Wizzie, you will have enough space in your party for a second wizard. In a custom or modified party, the best caster backline for BG2 would be a level 10 Swashbuckler / Mage, a Level 9 Berserker / Druid, and a Cleric / Mage multiclass. Your other 3 slots can then be filled with tanky characters, and even another thief if you want to get Thief HLAs. A 9 Kensai / Thief would be best as they get huge melee bonuses with Kensai which will apply to their backstabs, and can then overcome their no armor or gauntlets restriction with the Thief's Use Any Item HLA, and then two slots left for a pair of heavy armor melees, such as a pure Berzerker and an Inquisitor for more powerful than normal dispel magics and true seeing would be awesome.
Swashbuckler / Mages also get nifty elven chainmail later into the game giving them an even bigger AC boost on top of their swashbuckler bonuses while still being able to cast spells.
Pure wizards and thiefs on the other hand are weak sauce except for Edwin.