I'm only self taught, and have yet to sort out my own bottle cap template, but I'll see if I can help
You can actually use a grid in Gimp, which will help line them up, it's under the View Tab, you can set your own sizing.. Then there's "snap to grid" under the same tab, so if you're moving a layer, as you get closer it will kind of push it straight in to the corner of the grid square to line it up, hope that makes sense
To add more fonts you can download them, put them in your fonts file on your computer then if you restart GIMP they should be there, I think.. I have sooo many but haven't done it for a while.. You can do the same with brushes, even photoshop ones, you just need to paste them directly in to the brushes file in the GIMP directory where the program is on your hard drive..
There's a little bucket tool to fill in coloured areas, is that what you mean?? Looks like a paint tin
Hope that helps a bit, there's a lot to learn when you first start, I'm sure I use about 10% of what its capable of, but its fun, easy to use once you get the hang of it - and FREE