1 - it will be a dry lot, so hay will be needed, which is better with minis anyway, imo as they can be VERY easy keepers and tend towards overweight, which is not healthy
2 - likely none if you provide good forage (hay) - again, see #1 re: the issue of minis and being overweight
3 - see #2
4 - slow down. Unless she is registered and then proves herself to be of breeding quality, please do not breed her. The horse market is flooded with the results of overbreeding.
5 - a "run in" (three sided shelter) will be easily and cheaply constructed - you can google up tons of plans that would work for minis
6 - "can" and "should" are like "surivive" and "thrive" -- they are, by nature, herd animals. They *can* live as lone animals, but having more than one is better them. If you can afford two, get two....otherwise another buddy can work (goat, etc)....which also goes back to the question of breeding since you would need to be able to afford more than one at that point as well. Remember it isn't just about feed for two - but farrier, dentistry, vaccination, etc.