All of the above is absolutely correct :) My minis tend to foal at day 310-320. We watch ours on a foaling camera so we can be sure to attend the birth. Minis do have a lot more problems foaling so we are always there. Be sure you are not feeding fescue as minis have even more trouble with it then big horses. Big horses is recommended to take off fescue 60 days before foaling but with a mini I would 120 days.
Red bag deliveries can also happen. If it does get the foal out as quickly as possible by cutting the red bag open
Really educate yourself because usually unless your vet is really close its too late by the time they get there.
We up our grain on mares in foal starting about 90 days before foaling. Some mares though will start to go down in condition and we start sooner with them.