Haven't played this in a while but as far I remember the mechanics was similar to FOTR.

I.e. either defend against huge fleets in space if so stay close to the valedusa (just in front of it) as it provides repair and also put alot of point defense stuff in your battle line and also some extra repair ships so they cover your line. Be aggressive with your bombers and prioritize their repair ships and big threats (withdraw them to heal from time to time) and do use the ground to space gun. After you defeat the first wave it will be much easier as some enemies will spawn way back i.e. trickle in more or less alone, easy target for your bombers and letting you recharge shields. In FOTR a stack of 300-400 will very easily defeat an attacking 2.5k stack with none or *rarely* a few point-defense corvette losses, if you know what you are doing.

OR, defend on ground instead. Some worlds are super easy to defend on, build the shield bubble and stay within that and have say 3 artillery that you use to target enemy artilley as prio 1. I have fond memories of the AI assaulting with 100+ units and getting absolutely deleted with zero losses for the defender by the well-placed AT-AT, artillery etc. In this scenario you need to have some kind of repair ability, anything that lets you see farther is also good for the artillery, and place your defense (go all vehicle!) around the repair thingy.

Both scenarios require alot of pausing of course and issuing new targeting orders and ensure that you press STOP when you have perfectly positioned stuff so that your units don't break away and give chase (certain death).

I actually stood still and FFW:ed my last game in FOTR just because it was so enjoyable annihilating vast enemy incoming stacks on ground and in space, but you might not see it this way :)