27" was a wheel size that Schwinn and some others used here in the US for road bikes, IIRC, whereas in europe it was the 700C wheel for the most part (the 27" has mostly disappeared as the euro standards have taken over in road bikes even here in the US). 26" was mostly for mountain bikes, and since we started the bigger production of that size, became somewhat a standard. These days mountain bikes are more 27.5" (650B) or 29" (700C with fat tires essentially). 26" wheels are still found on some of the cheaper offerings, tho. Cranks depend more on your leg length, 172.5 mm are often the base length for mens sizing at least, altho sometimes that's a bit long, 175 is more unusual/for taller guys. I've used mostly 172.5, altho my emtn bike came with 165s. There often isn't much choice on a new bike depending on frame size somewhat, often something you need to change out for yourself if you want different.
I've used some of the better stem and seat post type suspensions, not the really cheap crap that's sometimes offered, and it's really a poorer experience compared to a proper fork or shock (shocks generally are rear shocks in purpose designed frames, we just call 'em forks for the most part as rigid forks on actual mountain bikes are rare). A little bit of reduction of bumps are good, but fatter tires can often do a better job of that than the gimmicky stem or seat post type suspensions....
Mountain bikes have evolved to have a more upright position generally, rather than a strict racer-boy cross country style as was popular when I got into it in the late 80s/early 90s. Comfort as we age does become more important, I have no desire to ride hardtails much these days. My first full suspension was a Moots YBB (why be beat) which didn't use an actual shock for the rear, but more a way of allowing the titanium frame to flex with less than 1" of travel. These days I use 150mm/160mm forks with rear travel of 100-160mm depending on bike. I'm one of those guys who has a sizeable investment in bikes....7 mountain, 2 road, mostly of the pricey variety with good quality componentry. I do take them off sweet jumps now and then, too.