Should I upgrade buildings to the maximum before I upgrade TH level?

Yes

Yes. Upgrading all buildings, defensive or non-defensive is very important before you upgrade your town hall.
Top priority in upgrading buildings should be your laboratory, spell factory and army camps so that you can have stronger troops, increased number of troops and powerful spells.
This way, you will be able to get a good offense team and increase your chances of winning three stars at war.
A good defense is also as important as aggressive attacking, so you also need to upgrade your defensive buildings.
Upgrading the defensive building is important before upgrading your town hall level because in a higher town hall, new buildings and upgrades will be made available and so, if your building are already maxed, you can focus your builders on upgrading them to an even higher level or building new defensive structures.