There's a lot of good inside knowledge here, Ohio, and I am just a guy from the PNW, so take my comments with a grain of salt. But I have skied most of the Summit County areas and I think that you need to tune the advice here to your goals. What are you trying to accomplish during your first ski week out west? Are you optimizing for skiing? Economy? Seeing every mountain in Summit County?
If it were me, I'd be optimizing for skiing and taking a jump in level while you are there. I'm not sure that I'd spend the trip driving around in a "vision quest" to see every resort in the proximate area of Frisco. Two reasons: (1) until you have been there, you have no idea how to process just how big these places are in relation to what you currently understand to be "skiing." You could ski 7 days, 7 weeks, 7 years at a single resort and not get bored (although if you are a local, it would be somewhat strange not to at least be familiar with the surrounding areas); and (2) if you are basically a green/blue skier, there isn't a really good reason in terms of terrain diversity to be running around from resort to resort, unless you want to sample the vibe or the respective base lodges. The greens and the blues are the runs where the areas are most similar. Unless you are talking about heading over to Vail to ski low angle stuff in the back bowls (which is pretty different from anything else), lapping marked green and blue runs is basically the same deal whether you are at Keystone, Copper, Winter Park or any other place in the front range.
Locals love their local no frills areas (I do as well), but the reality is that you'd probably be happy as a clam at Keystone for 7 days and it is very well set up for your scenario. If I were you, based on what you've said about your skiing, and the fact that you are looking to optimize for value, I'd probably ski the bulk of the trip at Keystone with maybe a day at AB tacked on toward the end of the week for a smaller, local mountain experience. Rather than drive around Summit County to ski basically the same green/blue groomers you just left, I'd get situated at a home base, and spend the extra time and cash on a pack of lessons. Especially mid-week, early season, you are likely to get a top-flight instructor for a semi-private if you just show up for a group lesson. If curiosity has you pining to check out Loveland, hit it for a 1/2 day on the way up from DIA or the way back to DIA. Ski Cooper seems like overthinking it for a green/blue tourist with a just a week. Not so sure about AB for intermediates. . . never thought of it in that context. But I'd lean on the locals here, if they say that you'll be OK, go for it for a day. It is a cool place and pretty different from Keystone just down the road. But my recollection is that the magic of Arapaho is not the intermediate terrain. I know that it is kind of uncool to say this, and I should be pushing you to ski somewhere cheap, local and "core," but you the truth is that Keystone is likely your best bet for this trip. There are acres and acres of long groomers with a range of pitch to choose from. They make snow if it is patchy. If there is full coverage, you won't exhaust it in a week and when you improve in skill and confidence toward the back of the week, there are plenty of new challenges to try that you might have been spying on the trail map or from the chair.
I might be projecting here - but driving around while on a ski vacation in mountain country just is not my cup of tea. Maybe that is because day hop skiing for us (Seattle area) means either a 45 minute drive or a 1.5 hr drive (I know, the east coast and midwest folks don't feel all that bad for us). So when I am on vacation, I prefer to leave the car at the condo and avoid things like packing the car and dressing in parking lots. But everyone has their own vision of vacation. And even in Summit County, where it kind of works if you don't care about driving around, economically, that play worked better 10-15 years ago, when you just rolled up to the window and bought a day pass. But now, the deals on multi-day passes almost force you to choose one collection of mountains or another.
Like others have said, there's nothing you can do about altitude until you get there and find out how it affects you. Drink lots of water, use the humidifier in your bedroom and go easy on the booze the first couple of days. Other than that, I wouldn't overthink it because you can't really change it.
Have fun. You will love it and I wouldn't worry about hitting every mountain in sight because as long as you are having fun where you are, you aren't missing anything. And there is always next time.