Dude... that is like the motherload of info. I just browsed their site and it's awesome. I think this might be exactly what I'm looking for in terms of variety and definitely price. Since we're basically novices on purchasing bikes like this, I'll say that we'll basically be riding on bike trails - like old canal paths around our area (and in others), so it'll basically be flat and smooth, I think. Would you recommend visiting some bike shops to get a feel for what we need and then ordering online or is something like that frowned upon? Based on the info I've given so far, is there a brand/model that jumps out at you for us already? Thanks so much for that tip.
I find there to be ethical issues with spending bricks&mortar store time and then buying online, so I can't advise that. If it's worth it to you to get someone's in-person sizing determinations... you kinda owe them something IMO.
That said: You can size bikes pretty accurately on your own. Leg length matters a lot, but also consider torso & arm length. My current MTB (mountain bike) would probably be a decent trials bike; it's got a relatively small frame and it's pretty compact but this means the seat's up quite a bit above the frame and the handlebars are on a long gooseneck and the bike is really twitchy and I feel like I'll crash just trying to get a drink when I'm going above 15mph. Yes, I bought this at a LBS (local bike shop) and it was recommended by size, and I call it a mistake and someday I'll sell it and buy a bigger bike. So obviously buying at the LBS isn't a guarantee that you'll get the right bike! Maybe they just really wanted to sell it.
If you're doing casual trail stuff, or pavement & gravel, don't get a full-suspension bike. The rear suspension is extra weight and cost and complexity that's for pretty serious downhill travel or for really heavy people (I knew a guy who rode casually but he broke bikes quickly until he got a full-suspension: he was 6'6 & 350#).
I personally mostly ride on the road but prefer a MTB vs road bike because bigger tires have more cushion and the front suspension helps with comfort too, and it's a more upright position. MTB isn't as efficient on the road... but I'm just trying to get exercise. I just won't go quite as far on the MTB in the same amount of time as the road bike (eventually sold the road bike already) and still get the same workout, just more comfortably. I ride with tires that are great for road & dirt but would suck on mud, but if it's really muddy out I'm not likely to ride. My tires are 26x2.1" with not quite a slick; they have pretty minimal road friction but still plenty of off-road traction (in dry). Most MTB will come with knobbies and if you mainly ride on the road even when you're just out for exercise you're still probably going to want to replace those, there's limits to not caring about inefficiences haha.
These days they've fragmented the bike market further and now have "gravel bikes" that from what I can tell are like old-fashioned cyclocross bikes. I have a preference for the wider flat MTB handlebars for more upright position, but you may differ.
It's been years since I shopped bikes. My advice would be to look for a bike with at least a middle-of-the-line component set; it used to be that eg Shimano had 3 lines, but now I think they have like 7 or 8. XTR is gorgeous light and perfect sure but super pricey. DX or XT are fine and more than sufficient. Or they were a few years back... basically think about getting the F350 XLT, don't bother with a platinum or king ranch, this is a bicycle. The analogy falls apart though because even the base model is reliable, but I don't consider the base component groups to be reliable - they'll work fine for a little while and get out of adjustment more easily or little **** will break on them. Buy decent stuff and you'll rarely have to mess with it.
26" vs 29er: Doesn't matter, really. 29" look cool and may have a slight edge in rolling smoothness, but I'd check tire prices and initial cost and base it on that. We rode 26" for decades and we liked it!
Fat tire (4" tires): don't, unless you're riding
on the beach or in snow, and then reconsidering doing that. Sand will get in everything and destroy it. When I lived in a beach town and often rode my bike to beaches, I literally carried the bike on the sand and flipped it upside down on the seat & handlebars to keep sand out of the workings. 4" tires are really heavy and expensive; the wheels are heavier and expensive; the extra rotating mass will start and stop more slowly.