It all depends on the model. Most are 240v, and the wiring connection is made through the outdoor unit.
If you're going with a multi-split setup (one condenser feeding multiple indoor heads), then you just need a single 240v connection with a disconnect near the anticipated future location of the condenser.
If you're giving each head its own condenser, you'll need many such electrical connections: one per condenser. Those'll take up a lot of room on your electrical panel; make sure it's big enough.
With this kind of cadillac equipment, make sure you're getting the absolute highest efficiency possible. The best units go up to 33 SEER and 14 HSPF. You're already going to be paying $3-4,000 per head; any upcharge to get maximum efficiency is always worth it. Don't compromise here.
Finally, be absolutely sure you select a reputable contractor who can demonstrate that they have installed hundreds of systems just like the one you're asking for. Also be sure they give you an ironclad warranty and a performance guarantee. The reason why I mention these things is that mini-split systems are pretty unfamiliar to most American contractors, most of whom only know how gas furnaces and conventional AC systems. You really need to make sure that your contractor knows what they're doing with this equipment or else you will be disappointed--guaranteed.