I am also TH8, but I started doing right away my teslas as soon as I hit it. I am barely mid TH8 and my 3rd tesla is about to be lvl 5. After that I start lvl 6. I have one worker dedicated to them.
My point is, I know what you are thinking, you will do them once you get to level 9. BUT, level 9 is not like 8 where you don't get new stuff other then more upgrades of defenses. At level 9, you will have to upgrade the spell factory, camps, maybe barracks, xbows. So I am guessing you will not have a worker to work on the Teslas for at least couple weeks, and they will just fall back even further. I would put 3 workers on them and get them done, but then it is up to you.
I also do not upgrade my collectors, but I think before I go into 9 I will do. Maybe while you are waiting for your teslas you can get your collectors caught up as well. I hear level 11 and 12 do good loot over night, so it is like one free army per night.

