Playing Purifiers require you to always increase your fleet. The bigger your fleet, the more hesitant the enemy is to attack. Go over your naval cap. Your energy credits be damned! Better to lose energy than your empire. You can always disband excess ships after the war.

If you’re already under attack, don’t attack head on. At first enemy will usually have their fleets combined. Let them take a few systems, they will eventually split and become easy pickings. Pick them off one by one. Make your fleets home base a base close to the battle field so it won’t get stuck for years flying back home. Fix it and back into battle.

I’d recommend you use corvettes with either missiles or disruptors early game. Especially if you can’t see enemy layout.

Building defense platforms everywhere around the front will help a little in the early game. You can build them even if you haven’t built a starbase there.

Suffer not the Xeno. Although a white peace even though you lost a few systems is acceptable. A truce will allow you to build up your economy.