How do building upgrades work during CWL?

Basically I just upgraded to TH10 and copied some war base online that I think checks out for now, and would really really like to do the CWL since i've only done it once before and that was like a year ago, but I've got some things to get upgraded to an acceptable level over the next couple days such as archer tower, cannon, and traps (all new defenses are currently building and from when i was in war base build mode, i assume new defenses in progress just show as already built in war?).

will i be able to upgrade buildings during/between CWL wars that will impact that or the next war?

is war matchmaking good enough that i'll likely not get a maxed th10?