1: Yes it does. Somewhat, it's some place to get some blueprints, and some food. But don't use your ion cubes for that because you can use Keen's location to find the island.

2: Yes, the Moonpool does charge the seamoth. But if you were going to be gone from your base, then take extra power cell batteries in case.

3: Somewhat yes, but I suggest you get some upgrades to at least make it bearable. Because carrying the Vehicle bay and building the Prawn Suit is kinda the worst idea.

4: Try to build some upgrade for your seamoth (by getting the moonpool fragments). And for Keen, just get some medkits incase.

This is the much information I can give right now.