Questions about multiclass

[hexzero13]

Sorry if this should be in the main forum, I figured it fit more with class builds.

So to preface I am excited to try Deadfire, I just bought POE1 like a month ago and am almost done with it and loved it. In Deadfire I am excited to try multiclass. Can somebody explain to me how far up the skill trees you can go for the 2 classes? Like say I did a Paladin/Wizard...what level spells can my character learn up to from the Wizard school? And it says you learn things slower...how much slower? Is it like I won't even have level 4 wizard spells until max or something? Or is it just a level or 2 behind? Thanks in advance!