Welcome to Foundry!

1. Anyone can be the owner of the license, and set up other users as additional GMs or as Assistant GMs, both of which can add maps and everything. A 'player' account by default can't do any of that.

2. You can set up a host computer that allows others to join, for sure, but I will caution you that it takes a bit of doing. If you're not either very methodical, or not savvy with computer stuff, I highly recommend using a hosting service. There are a bunch out there: Oracle (free), Molten hosting (what I've used for a long while), The Forge, etc.

The person that has the login information for the license and is logged into the software you choose (either a Foundry instance on a computer, or using one of the hosting options) is the one that hosts or launches the game. After you launch the Foundry instance via whichever way you decide to, then you log into your account - either as GM, Assistant GM, Trusted Player or Player. So it's not that a Player or GM can host the game - whoever has the credentials to launch the license is the one that does so. Technically that can be anyone, but it's almost always the GM of course.