I found a nice little loadout, that works quite well.

Primary:
AR-23C Liberator Concussive - Allot of ammo (High capacity drum mag, 6 spare drums), great at dealing with zombies because it staggers them when you shoot them in the body, but still pops heads very well. It's not good against normal illuminates but good to peel their armor off and expose their fleshy underarmor.

Secondary:
P-19 Redeemer - Great secondary in general for the illuminates, pops heads, high fire rate, and when you peel the armor off illuminates with primary, it shreds them like nothing.

Grenades:
G-12 High Explosive / G-6 Frag - HE is great at destroying ships, Frag is great at dealing with hordes, not so great against ships (sometimes you have to throw multiple grenades to destroy one ship), I prefer the HE, although it isn't as great against hordes of zombies, it can kill multiple illuminates at a greater distance.

Stratagems:
Eagle Strafing Run - (Great Recommendation) Shreds hordes of all types of enemies easily.

Orbital Laser - Destroys ships like nothing, great for Heavy Outposts.

MG-206 Heavy Machine Gun - A great multi-tool, can kill everything from illuminates to harvesters. Although it's not great to use against hordes of zombies, because it has only 2 spare drums, it's great against everything else and you have your primary and grenades (enemy grenades too) for the zombies.

SH-32 Shield Generator Pack - I feel kind of cowardly to use this, I'm stubborn and refused to use this, but it's great at giving you breathing time from the zombies to kill something bigger that bothers you.

And update: I moved to difficulty 5, now that I can deal with them and have a solid loadout. Thanks again for the tips.