-no real difference between units should just buy them all no strategy due to this
-clicking basically worthless
-just upgrade all buildings and units evenly no strategy
-can't do anything with level bonuses like equip no strategy
no this is too repetitive
Easy way to beat the last few levels: spend all your money on cheap cavalry down to one lane. If the lane is occupied, start over again until you get a lane that's free. You'll bring down the enemy's moral to 0 very fast. Even if you can't defeat the few monsters that the enemy spawned, you'll still win.
Easy way to beat Legendary mode: keep spamming Shield Maidens. I found this unit to be the most cost efficient. Invest all your exp in skills that upgrade the Shield Maiden, e.g. every spear upgrade and every infantry upgrade. Also try to rush out War Taxes, this will speed up the process greatly.
The only weakness of Shield Maiden are archers and skirmishers in the later stages. You can use Lancers to deal with these efficiently, and in later stages you can also mix it up with some Shieldbreakers.
Good luck!