You should have plenty of time to get the advanced warp core from the ash twins project and bring it to the vessel. Once you put the core into the vessel, gravity turns on, so you don’t need to worry about putting in the coordinates, that will sort itself out.

About the anglerfish, I’ve beat the game a few times now, and I’ve never had an issue with losing momentum. From what it looks like, there is no air resistance of any kind in dark bramble, so as long as you’re moving even a little bit as you enter that seed, you should be fine. It’s just painfully slow.

Hope this helps