I don't mean to flame you, Zyxpsilon, but that's some pretty horrible advice you're giving out there, IMHO.
Usually to me (and depending on many other factors or situations) this 26PQ sounds like the perfect steady supplier of attack Fleets; focused on Factories, and cranking out the numbers!
It wouldn't hurt to have a little bit of industry going on -- to crank out transports and freighters -- but to focus a size 26 planet on industry alone is kind of nutty.
You don't really need that much industry. Hell, you don't often need that many ships. Or, I don't, anyway. I try to make do with fewer, better quality ships, and only really need a few planets focused on producing them, which does not need massive amounts of real estate . Usually, my home planet suffices until the mid-game; by then I have captured several other civilizations' capitals, one of which will become a second manufacturing capital.
The Precusor Library is just that - a bonus, unless you can afford locking half the tiles along with the technology capital there too.
But you'd only be using 3 tiles of 26; with a tech building, tech capital, and research coordinator, you have a great research base. That's a better research output than you'll get from a lot of lower quality planets focusing on research.
You'd otherwise need two Morale and possibly Markets too to lift it above feasible 'values' if pop grows beyond the 18b mark.
You don't need any morale buildings, though you have the approval tile if you really feel it's necessary. Going to 18 billion is too high anyway.
Otherwise, boost it above the 20b and use it as a launch point for Transports every 5 to 10 turns or so.
By going to 20b, you are making your people unhappy. If you want them to breed faster, you have the recruiting centre and/or fertility centres (though the latter is mostly obsolete now, IMHO).
It mostly depends also on the exact location. Nearby an emeny's borders or nicely tucked way inside your own territory. Any resources proximity can also tilt it towards a steady Constructors output.
"Borders" mean very little in this game, in my experience. Besides, if this is made into an economic world, filled with people and stock markets, your borders are going to expand quite a bit...
It could also serve as the 'Trade-Goods' or 'Super & Galactics' quickie builder IF the overall manufacturing potential is already there.
That would be a major waste of the space, I think. The best place to put them, in my experience, is smaller planets where there is little point focusing on econ, research, or mil, because it'll be crap regardless. Whereas, with this
planet, it makes sense to be as efficient as possible.