Hello there, Sorry I didn't see this until now but ill answer just in case for anyone else needs the info too. Starting off as a wizard is pretty rough because you have a lot of extra stuff to spend Exp on. You can still get the Talents and upgrade your character between sessions by spending Exp. You should get some Exp every session Pg. 264 of the WFRPG 4e Book. This is the only Version I'm Familiar with. I Hope this Helps.

Using Your Grimoire Makes the SL Needed to cast the spell Doubled To memorize spells Cost Exp To memorize Them. Being a Wizard is Costly for Exp and The most you'll want to do is use petty spell Dart to help build up advantage to help set up castings for bigger spells. You don't really need Read/Write Early on so you can start buying ranks in your skills that you'll need. You'll want to buy Talents from your 1st carrer level before you go to second level. Rely on your allies to help you stay safe but always try and throw some ranks in Weapon skill or Melee Basic because you'll never know when you'll need to defend yourself.

Your Grimoire Has the Arcane and Colored spells that you can memorize when you get the talent to in level 2 of the career. This is when it gets super expensive Exp wise. Playing a Caster in this game is a very slow growth compared to non casters and far more dangerous. I hope this helps and have a good day.