I'm in the same situation. I first bought all the new defenses(air defense, wizard tower, tesla) and upgraded those to th7 level along with archers and barbs to level 5 in the lab. Then I took care of the walls to level 6, and am currently working through maxing defenses at th8: splash damage first(mortars/wiz) then everything else. Once I have all the defenses maxed, I plan to farm for level 7 walls and use the elixir to max all the lab upgrades.
Get your new wizard tower, air defense, and archer tower up to level with the rest. Also getting Mortars to level 6 is big since at that point they can single shot all level archers