Hi, and welcome to the world of minis!!! Here is my advice regarding your questions.
For someone just starting out with mini's, MUST you have to buy 2 mini's at the exact same time? Can you purchase one and then within a couple of months get the second mini?
I think that can work out just fine, so long as you do plan to get another mini soon. Doing it that way, getting one first, then the other, will give you time to get to know the first one and bond well with him / her before bringing in your other mini, plus give you time to get used to the ins and outs of caring for a horse on your own.
Also if you purchase a stallion, what could he be put with? Another stallion, gelding! Obviously not a mare unless your breeding.
Often times, the only horses a stallion can be safely kept with is actually a mare. Many times, stallions will fight with geldings and
most times, they will fight viciously with other stallions. Your safest bet for two horses most likely to get along would be two geldings. When it comes to having an enjoyable horse, I think it's pretty hard to beat geldings!
What about if you purchase a mare in foal, will she be ok alone until her foal is born?
If the foal is due fairly soon, that should work out fine. Keep in mind, if she has a colt, you'll probably want to geld him, or will need to keep them separate by the time he's about 1yo.
Good luck!!! Minis are so much fun
:yes