Hello! Here are some answers for you.

1. You should not bring newly potted plants inside now. The best thing would be to buy them at the right time for planting. If you're buying online, you can buy now and request that they ship at the right time for planting in your zone. If you must buy now, you can keep your new plants in an unheated garage until the ground thaws and you can plant them. This is likely in mid-late March. However, if it arrives fully leafed out, then you want to protect a JM until the risk of spring frost is past.
2. Emperor 1 is a very nice red maple. I presume the reason you've got it picked out is the common description that it leafs out a few weeks later than bloodgood, and is superior for avoiding late spring freeze. Either way, it's a nice tree. I'm linking you (below) to the Essence of the Tree website 'Maples for Cold Climates'. Maybe you'll see something else that catches your fancy. :*)
3. You're looking for both good orange color and Z5 hardiness. In general, you can look to japonicums for spectacular fall color. There's one called 'Emmet's Pumpkin' that is a fall orange. You should check them all out.
4. If you're buying a named JM, it has been propagated by grafting. My guess about what you're asking about is that some vendors will refer to very young trees as '1 year grafts' or similar wording, which just means that they're very small and tender, (and less expensive than a 1 gallon plant, which is 2-3 years older). It may look like nothing more than a small twig. If you go for a young graft, you'll have to baby it a long for the first few years. If that's something you'd be interested in, go ahead and ask and we can tell you what extra steps you'll need to take. You probably wouldn't want to plant it out in the landscape right away though.

I hope this helps.

Here is a link that might be useful: Maples for cold climates

Another ap cultivar noted for orange fall color is 'Hogyoku'. You may want to do some searches on it as far as your zone is concerned. They do fine in zone 7a.
AL