First thing first, good job getting thus far with only 3 builders
1) Is your clan active in donations ? If so, you might want to consider centralising it to make it unlurable.
2) Lv6 Tesla at TH8 indeed has the highest DPS among all single target defense, but the best defense for resource is actually the wizard tower, so I wouldn't give the tesla such a core location.
3) Reason why your base is vulnerable against giant/healer is because your AD is really exposed. I would recommend you to push out the tesla, together with the extra 3 walls near your town hall, and push in your air def more.
4) I would suggest you to totally remove townhall from walls, farming is the way to go for now until league bonus is improved. stay around 1400~1500 for th8 loot.
5) Try to create 2 spacing T junction to account for wb's new splash radius.
6) I would recommend you to fully max out th8 before moving on, and you really should save up gems via achievement and obstacles for 4th builder.