Here are a couple of very helpful links especially in case for future multi-classing:
Spell slots from multiclassing
https://fexlabs.com/5eslots/Prerequisites (here you can also see which caster classes require which attribute for their spellcasting) etc. pp.
https://5thsrd.org/rules/multiclassing/For everything else, a general and detailed insight can be found here:
http://dnd5e.wikidot.com
