1) 26 vs 27.5 vs 29. Obviously the taller the tire the easier it will roll over stuff. 29's seem to be pretty standard now and it sounds like 27.5" is a newer size for mnt bikes? Thoughts on the three?
This is a hot debate right now and will continue to be for quite some time. I'll try to save my opinion and bias for the end. There are exceptions to every rule, but here are the generalities:
Smaller wheels (26") are stronger, slightly lighter, and are generally better for handling and carving turns. However, they don't roll over bumps as well. Larger wheels (29") roll over stuff really well at the expense of a slightly higher center of gravity (only 1.5") and slightly less exciting handling. Granted, the design of the bike has more to do with handling than the tire size, but I've yet to ride a 29er that carves like my 26.
Downhill bikes generally run 26" tires. XC bikes generally run 29" tires. The new trend is for almost everything else to run a 27.5 Shorter guys often have a hard time finding a 29er that fits them well, they often feel to big. 27.5" is supposed to be a compromise between the two. Personally, I think changing wheel size every 3 years is a gimmick from the mtb companies to convince you that your old bike is out of date and you need to get with the program and get the latest wheel size. Currently the rage is 27.5 (also called 650b). There's a guy at my work who's a noob rider, but he swears his 650B is light years better than his old 26 and 29er. He reads a lot of MTB mags, and they tell him it's the best of both worlds with zero compromises.
when 29ers came out, lots of people jumped to that wheel size because 26" was no longer cool. Now, 650Bs are all the rage, and 29ers aren't very cool. You'll have a tough time finding new 26ers and you'll have an easy time finding used 29ers (because they're all dumping their 29ers to get the latest 650b). Ride a few, you'll see what you like, but keep in mind that bike geometry is king before tire size.
My opinion:
I love popping off every rock and root in the trail, and handling is my #1 priority. Plus I'm short and I want a low COG. The 26" wheel fits my riding style best for me and my size. I feel like my COG is way too high on a 29er. A 29er would be awesome for me for a long distance xc ride where you just kind of weave through the hillside with lots of climbs and you don't really attack the downhill and flowy sections.
2) Tubeless Tires - I've never dealt with them. How well do they seal up? I'm guessing they are lighter since you don't have a tube in there. Thoughts?
I'm running tubless on one of my bikes and tubes on the other. They both make me smile when I ride. I haven't decided which is better. Tubeless is not usually lighter than running tubes. I can feel a difference with the contact with the ground, but it's minimal. I'm fine with either on my bikes.
3) Xc, trail, all mountain, enduro, freeride, and downhill... of that bunch Trail/All mountain sound the most appealing. I'd be interested in XC except I have a feeling they don't hold up super well to abuse and if I'm going to spend the money I want something fairly stout. Enduro, free ride and downhill from what I can tell would be overkill for my riding style (or lack thereof). I'm just an out of shape dude who is pretty slow everywhere but wants to get back in shape and have some fun while doing it. Am I correct in thinking a trail/all mountain is the right fit?
yeah, I think trail/all-mountain would be a good fit. That being said, they're just buzzwords. Bikes don't necessarily fit into one neat little category. It's all marketing.
XC will focus on lightweight and ability to travel long distances. They're still strong bikes, but they're designed for 15+ mile rides. On a long ride you'll appreciate the lighter weight. But you're right, when you go lighter, you either give up strength, or you pay through the nose for it. Also, the geometries of a XC bike will be more race-like (in a bad way). The head angle will be steep, more like a road bike than a chopper. This makes steering on the downhill a bit twichy, but very stable for climbs. An XC bike will climb better than any other genre.
Trail/all mountain is the swiss army knife. Not the lightest, but not the heaviest. Can climb ok, can descend ok.
Enduros have a lot of travel (typically 6"), but can still be climbed on relatively easily. This is probably overkill for how most people ride their bikes here in Utah. There aren't many trails around that you'll utilize your full 6" of travel.
Past the above, I have really no desire for electronic parts, dropper posts, etc. I want to keep it as simple and reliable as possible.
Remember, most of these are designed to convince you your current bike isn't good enough and you need to get with the times and sell your old bike and get a new one. They each have their place, and most of them do offer a slight performance increase, but they're not necessary to have fun. The main technology that I can't live without is a dropper post. That's a complete game-changer for me, but they're expensive, incompatible with super old bikes, heavy, an extra cable, and not everyone thinks they're worth it. I will never have a bike without one again.