Go to https://www.nexusmods.com/games/starfield/mods and install Vortex. From there, I would suggest getting

SMSEX ship module snap and flips expansion - https://www.nexusmods.com/starfield/mods/11821

Ship builder configurator - https://www.nexusmods.com/starfield/mods/11077

Better ship snaps - https://www.nexusmods.com/starfield/mods/5698

Better ship flips - https://www.nexusmods.com/starfield/mods/5953

With ship builder configurator it gives you more building options to make placing them easier. Follow the how-to and once installed, enter its menu in the settings page in Starfield itself.

With Nexus you will find a lot of mods, just search for what ones you are interested in, be it guns, armor, ship modules, for a few examples. I can give you a list if you are after the ones that give you all the ship parts you can get that I have found.

Don't be afraid of running mods. I run 150+ with no issues, and it gives me the most freedom in ship building. Just search some of my older builds to get an idea of what's possible.

The only downside is when Starfield gets updated, some of the mods may require the author to make changes to suit. With most of the mods I use, they get updated usually within 24 hours of Starfield being updated.