Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

Hello!

I'm a little confused about how the mutli classing works on BG.

I'm currently playing as a wizard with a few levels in master alchemist...it says that I gain spell caster progression; but my question is -- do I also gain caster levels? Or are the two things totally different?

Would be super grateful if someone could clear this up for me <3

Yes you gain caster levels, Thaumaturge is a 5 level PRC giving you 5 levels of spell progression, spell progression always means caster level progression (but caster level progression doesn't always mean spell progression, for example practiced spellcaster or spell power raise caster level but do not give you spell progression).