1. As it stands, fonts have to either be made by hand (tedious, we know) or the fonts that comes with RMMZ. Let us get back to you on this ASAP... we may change that since we hadn't considered it. For now, please bank on using what comes with RMMZ or creating your own.
2. You can use the tool to create assets, but not the assets that come with the tool.
3. We actually answer this question right here. If the pack you linked us is a free community available resource, you can use it, even if you've already created it. If this is something you've always had private, or had it private prior to the game jam, you cannot use it.
Hopefully, that helps!