I would definately make sure that your foaling kit is close to where you expect the mares to foal out - and that all the necessary items (you can do a search here and find info out about what should be in your foaling kit) I think that having TONS of lube is really important because you can NEVER have enough lube if you need to reposition a foal and without it it is very difficult.
Read the books, watch the videos -- KNOW WHAT IS NORMAL - BE PREPARED FOR THE ABNORMAL and be ready to assist - I can guarantee you that you will probably not get a vet to your place, or get your mare to a clinic in time to save the life of a foal should that baby need a little assistance - being slow to react or squeamish is not the type of attitude you can afford to adopt when a foal is coming into the world.
A good exercise to perform is to put a stuffed horse in a black plastic bag and pretend it is a real foal, feel where the head is, run your hands down the neck to shoulders, rotate the legs in the directions that a horse can move it legs - know what the front knee feels like and which direction the leg should bend -- all that sort of structural information will be helpful if you need to assist in delivery
Being overly perpared - foaling kit, truck hitched & ready to go, and then being vigilant and checking your mares very frequently is all part of foaling out minis. I have spent many, many nights (actually as much as a month) sleeping in the barn, in the stall with an expectant mare - thankfully with foal monitors, cameras and all the other fancy stuff these days I don't have to do that anymore, but my point is -- I DID IT. It is so easy to miss a birth, and it is not unusual for a miniature to need a little help - and it can save the life of your foal not to mention your mare.
Bottom line, foaling out miniature mares is not for the faint of heart - it is a wonderful experience when everything goes right - and it is a haunting one when it doesn't.
I am not meaning to sound harsh - you are no doubt trying hard to find out all you can before your mare's birth - it is a stressful time, and there is no "magic wand" that will tell you when you need to be there -- I have been foaling out miniatures for nearly 30 years and have brought 100's of babies into the world over that time; and I still get a lump in my throat when I see my mare acting as tho the time is near - We lose untold hours of sleep monitoring them (and yes, I have a job to go to - thankfully my hubby and I are on opposite shifts so we never leave the mare alone, if this were not the case I would send my mare to a foaling facility)
Don't be afraid to call for help - there are many of us here who are more than welcome to take a phone call at anytime to help save the life of a mare & foal.