Holy crap man, talk about firing off the questions!
I'll try to answer them for you.
1.) Denver is one of the metro areas that is fairly close to the resorts. Most of them are around a 90 minute drive. You can give 10-15 minutes for some and others add 30. Winterpark, Copper, Keystone, Loveland, A-Basin, Breckenridge, Vail, Beaver Creek are the heavy hitters. There is also Echo mountain, but it's an all park place and doesn't get the snow the others do.
This is the land where the season pass deal was invented. You have the Epic Pass which gets you Keystone, A-Basin, Breckenridge, Vail, and Beaver creek for around $600. For a bit less you can get a pass without Vail and the Beaver and there are variations where you get 10 days at Vail and Beaver with a full season pass at the others. Prices vary. Breck has a world class park as is consistently rated a top 3 park by ski and snowboard magazines every year.
For somewhere in the neighborhood of $450 there is the Winterpark/Copper pass with 6 days at Steamboat. Called the Super Pass plus. Not as many resorts as the other, but I find all three to be fun while the Epic pass has a couple that are "meh" to me. Parks are not as good, though I believe Copper has been stepping it up. Still, they lag behind what Breck and Keystone offer. These resorts are not all grouped together like the others either. Steamboat is a weekend trip. Winterpark is North of 70 off of US 40. Copper is in Summit County just off of 70. Breck, Keystone, and A-Basin are in the area, with Vail just West over the pass. So you can play a bit of the traffic or snowfall game with this pass.
Loveland is all by themselves. It's a smaller mom and pop resort but has great terrain, a long season, and some of the higher snowfall totals. Park is not much, so if it is a priority, you'll want to look at the others.
Compared to Cali, the ski areas do not have as steep of terrain. The snow won't stick to it because it's so light. 45 degrees is about tops with some stuff tipping at 50 but not for long. The snow is so light that when you get the big dumps of over a foot, it's pretty amazing. That amount of snow overnight doesn't happen much though. What does happen is you get days on end with 4-8" of snow coming down, adding up nicely. Finding a good stash at a resort is key. Since the report can say 6" but after 5 days of this, you got more like 30" to be had. It stays cold so the powder will persist as long as the wind doesn't wreck it or get skied.
2.) Denver is pretty much a party town for a 20 something or those who refuse to quit. One of the accessible cites to party in I have been too. Tons of bars and clubs downtown. All within walking distance of each other. Great on a warm summer night. Fun in winter too. Regis has a few local bars right by it. The Music Box is on of them I believe. 44th and Tennyson area is close by and has several spots to get your drink and grub on. Regis is in a decent enough spot. Much nicer than it was 20 years ago.
3.) Driving in winter is much easier than in California. The colder temps keep the snow from packing down to ice. You've ran into chain control in California right? Well you won't here. I have chains in my vehicle and I have used them a grand total of zero times in 21 years. The snow does not pack down to ice like it does in California. Sure it will get icy, but just not a sheet of it like in the Sierras. If you have an AWD you'll be fine. In fact a FWD will do. It does help to put on snow tires. I drive FWD with studded snow tires in winter. Also, it does not snow much in the Denver area. Around 60" on average. You get over 300" at the Divide and west of it. Most of the time it'll be dumping at the ski areas and sunny in Denver. The drive usually consists of around 20 miles of driving in the snow, give or take depending on where you are headed. The other 60 miles is dry pavement. Sure there will be snowy drives from start to finish, but it's more of the exception than the rule.
4.) Yes it gets hot. Lot's of 90's. Kayaking, hiking, rockclimbing, mountain biking are all popular. There are some scooter gangs too. When it's really hot in town, the mountains provide relief. It's a quick drive to 10k ft where it's much cooler and pleasant.
5.) Again as mentioned 60" a year for snowfall in Denver. So there isn't much. It also generally melts off within 1 or 2 days after the storm. You'll be fine to drive out. I'd take a more southern route to try to avoid snow storms on the way. I40 to I25 would be a decent way to go. The other option is to link up with 70 from Vegas on I15 I believe. It kind of goes against my advice, but I70 in the winter is fairly tame. The road crews do a good job with it, and you usually don't get much snow until you get to the Vail Valley anyway. You do go over a couple of high elevation passes thought. Vail Pass and the Eisenhower tunnel. Keep that in mind if you vehicle is taxed towing the trailer. Probably best avoided. I won't recommend taking I80. The stretch through Wyoming can have some awful ground blizzard from blowing snow. When that happens visibility sucks, the roads get super iced and shit gets sketch. I got stopped outside of Rawlins Wyoming one year in winter due to ground blizzard and vehicles log jammed up. Due to visibility there wasn't much time to stop on icy roads. I did it. A semi coming up behind me had the same thing, except he was skidding and I thought I was fucked. Fortunately he was able to get in the emergency lane and just missed barreling into me. I've had a second experience that was similar on this stretch. I now avoid it in winter...