It's really nice!!! I'm not a fan of underwater bases though, simply cause I don't like water... but you have done a great job. I love the fact that you placed item frames in the floor as arrows to indicate where everything is. If you allow me a sugestion maybe you should try building some AFK farms (maybe you did but i couldn't find them) that way you can spend more time building and less time gathering resources.
Download The ZIP file, then double click to open it. The world file is in there. Go to your saves in .minecraft and drag the world file in your saves. Then this should automatically put the world in your worlds. If this is too confusing you can also search up on youtube how to do it. Also, thank you for the support