Beating the First Limited Gold level: 5 Priests, 2 Rifle Men, 4 Mace Men. You will need to buy the buildings that increase your population. Also upgrade these 3 units. You should be able to beat the level without losing any units if you do this quickly enough.
On the limited gold levels either:
a) Take away the enemy priests or
b) Limit their f*cking gold
It's almost impossible to beat these damn levels when they spam instant masses of units and mass heal them as well.
Putting 2 missile frigates at the bottom and then 2 at the top, followed by just spamming missile frigate(or anything else) at the bottom will make the computer only send ships to the bottom, leaving the top ships to destroy the mothership. Just saying.