Well, there are a few different ways that that can be addressed. But, before I speak directly to that, on the subject of whittling down the over 4000 ships, did you consider just raiding the guard posts and/or the command station? That "frees" the ships that were on guard duty, which means that they then are likely to come over to your planets if you aren't right on their plants at the moment. That might not sound like much, and in fact in some circumstances could be a hugely bad thing, but if you play your cards right that can mean you're fighting their forces on your planet near
your turrets, rather than on their planet around their turrets, which is an immense tactical advantage if you can survive their onslaught.
Tangent aside, here are various ways you could go about this; various techniques could be used individually or in tandem:
1. You could use lightning warheads to clear the immediate wormhole area, freeing your guys to come through, but that comes at an AIP cost.
2. You could use EMP warheads to freeze the turrets for a while, giving yourself 30 seconds (per EMP) of free reign.
3. You could bring fleet starships along (light, flagship, etc) with some bombers and fighters to boost their strength when attacking the turret balls (that only works so well).
4. You could just leave the turrets until you destroy the command stations on all the adjacent planets to your target planet, at which time the turrets will go out of supply and will be laughably easy to kill because they won't even be able to shoot at you.
5. You could build a force field generator of some sort and group-move your fleet around with that on the enemy planet (it can go through wormholes), so that you're hurting the AI turrets without them obliterating you. But, your firepower would go down by 75%, so that's pretty harsh. Including fleet starships under the forcefield would help, but only so much.
6. A mobile repair station fully outfitted with tugs can really help with the survivability of your ships in a situation like this.
7. If you have Zenith Bombards, those can take out turrets from outside their range, which is immensely useful although expensive in metal and crystal (and you still have to get them to an initial safe location).
8. Speaking of getting your ships to an initial safe location, you can use transports to do that, which are now knowledge-free (in the latest betas).
9. In general, I would recommend holding Z+X every so often, to see the enemy attack range circles. Unload your transport outside of any of those, then move your ships to attack turrets that are just under
one big circle of ranges, rather than under the intersection of 2-3 partially-overlapping turret balls. Basically what is being shown in that one tactics video on the videos page for AI War. If you choose which turret ball to attack based on that sort of thing, then you'll take the least amount of damage possible at any given time, which hugely boosts survivability.
And... I'm sure there are other things, too, that can be done. But hopefully those are a good start.
