The basics of Gleba

If you don't want to keep running out of seeds you'll need to process fruit in a biochamber, preferably with productivity modules.
You unlock the biochamber by "researching" the biochamber technology by crafting 10 nutrients (you need to harvest both tree types to unlock the biochamber tech)

Surprise! You barely get anything from processing fruits into metal, you need to grab that bacteria and cultivate it in a biolab to make more if you actually wanna go anywhere.
You need bacteria cultivation tech for this which requires you to craft bioflux which requires a biochamber.

Biochambers are pretty straight forward, they are like assemblers but need nutrients to work and you need them for everything organic on Gleba.
There is one thing that's easy to miss which is that they don't use electricity and use nutrients as a replacement, what this means is that modules that cause a change in electrical consumption cause a change in nutrient consumption in Biochambers.

Yeah so you might have noticed you'll need one morbillion ever precious nutrients if you don't want your factory to completely stop, you'll want to get ever precious nutrients from spoilage (made in an assembler and not a biochamber) so you'll always be able to produce it and also from bioflux (in a biochamber) since it's the only efficient way to mass produce the stuff.
I'd recomment you transport the stuff via robots to save yourself a headache and a half.

Devs want you to use the Holy Heating Tower so you'll use the Holy Heating Tower, unless you import uranium I guess.
Sacrifice your exess stuff into the Holy Heating Tower, spoilage and seeds are the things you should be burning the most and you should also set it up so that rocket fuel is sacrificed to it if the heat that gives your factory life gets too low.
Despite the 50% penalty you'll want to place solar panels to make getting back to production easier in the event of a power outage (unless you want to move everything through burner inserters).

There's no oil but you can make most oil solids from spoilables.
You can’t make explosives though as that requires coal. (Gleba tech will later allow you to make it from carbon/sulfur)

Yeah so Stompers can ignore most geometry and kill an entire factory wing in a few seconds so you'll need one trillion turrets everywhere, good luck!
You'll want bullet turrets since the devs force you to use them with resistances and you can't use flamers... or mines... but hey you can import tesla turrets! If you can't do that and don't have the iron for constant bullets (which chances are you won't in the early and midgame) you might have to settle for laser turrets. Either way invest in turret DMG tech.
You also can stall Stompers indefinitely with a shielded tank and repair packs since they can't hit bots, you should use this same tank to run over all nest in your spore cloud to significantly reduce the attacks you get.
You'll succeed in automating defense when you deal so much damage they fall over before they break anything.

You get eggs from spawners and stomper shells, you can duplicate them with nutrients and need to for science.
You should keep turrets around areas with eggs since they spoil into enemies and have a system where eccess eggs get Holy Heating Towered

Once you get eggs from Nauvis and process them to the better soil you'll end up with way more Yumako/Yellynut than you'll need, burn it for infinite power.
Don't be like me and completely forget this is an option.

Yumako mash: 3 minutes
Jelly: 4 minutes
Nutrients: 5 minutes
Pentapod egg: 15 minutes
Yumako/Jellynut/Gleba science pack: 1 hour
Bioflux: 2 hours

Become one with the swamp or it'll eat you.