I have not posted a lot since it's still being worked on. Though have gotten those things fleshed out in my progress.

1.) Everyone will pretty much be together as they go through the maps, with dice rolls etc. There will be character building and personal development as they travel through a spacecraft together and land in towns. So no, you will not be able to acquire your OWN space craft, though you can acquire your own mecha (As long as your roll succeeds).
2.)The six listed for use are the only ones available for use, but there will be a mass NPC of mechs in the story who are hostile.
3.)Grounded and Non-Grounded are actually quiet simple. You are traveling through space and in space there is nothing beneath your feet. Basically you float/fly/jet etc. Some can only be grounded on a flat surface while others cannot or some can do both.

The spacecraft will probably be a small transport with minimal weaponry attachments. I'm waiting to see how many people would be interested be for I make final details. If there are a number of people, there should be a bigger craft. If it's a few then the average transport should be plenty of room to work with. 

Let me know if you have anymore questions. This is an Interest Check and not a finalized plot.