That's just how stellaris calculates bonuses, not much I can do about it.
I am also aware of diplomatic weight. There wasn't a quick easy solution, if any at all.
Because when pop is doubled, now 2 bureaucrats are doing the job, in theory giving twice as much admin cap. So I could have just not touched it. But then player can just ignore admin cap for the rest of the game. (at least back then when you didn't have outposts). On the same thought, I need to add some kind of limit on how many outposts one can have, so problem stays. That's why I added only district, so players would still somewhat invest into developing administrative infrastructure, while not applying it to pops so it wouldn't be a big problem. Might need to remove it completely.

Jumping the fleet:
You won't be able to if it has starbase. I'll be reworking some stuff with that.
Which building was it? Might have missed it. Best way to help me catch if there's a bug is to provide save just before it occurs so I can easily recreate it.

Removal is easy to add. I'll do it shortly.
hmm, I think I'll add option to megastrtucture to make more.

You can't get terraforming, since you are not supposed to have planets anyway. I had forgotten about terraofrming candidates. Sounds cheesy though. "We are going to terraform this whole planet into habitable one so our farms on ships work better". Why not just use the tech to improve production on ship directly.
Thinking of doing exclusive megastrcture projects for the fleet. I have idea for two. One for transportation, another for resource bonuses.

Thank you for a good reply, apart from not being able to build Civilian Vessels fast enough, not finding use for most ascension perks and unable to build Megastructures, the game I'm in now is going fine.
I'm at 8xPopDoubling and alone as the custodian on the galactic council, I just decimated the Gray Tempest and a Fallen Empire, the year is closing to 2400 and I'm more than ready for the coming 2xCrisis.
Thank you and keep up the good work on this fascinating Mod.

I just tried to replicate the jumping problem and found something new, jumping to a system NOT fully serveyed worked fine, after failing to jump to a system that was fully serveyed, both systems had allied and neutral ships currently serveying.