Stumpjumper for sure, but try it first, you may not like the feel of it. They're relatively neutral, fun to ride, more all-purpose. Also has good, quality parts.
I would suggest against building your first bike. One, it's going to cost more than a pre-built. Two, you need specialty tools. Some are cheap, but you need a headset press, $55 or so. Three, if you screw up, you're done. Buy the headset press, and get the headset halfway in crooked, forget it. You need a new frame. Put the BB in the wrong side and start wrenching, crossthreaded shell.......go buy a new frame. Some things you can do with a screwdriver, but other things........not unless you know what you're doing and have the money to burn if you make a mistake. If you do wind up going self-built, have a shop do the technical stuff, like install the headset, measure, cut, and face the fork (do NOT try that without a proper, true, cutting guide. Cut it crooked and install it, you'll blow the bearings out of the headset in just a few rides), put the cassette on the wheel, the major stuff. Then do things like install brakes, cables, the rest of the build, yourself. Read up. Get Barnett's Bicycle Guide and read it.
Honestly, I don't know that a full suspension bike is going to do much for your foot slipping off. XC rear suspension isn't meant to make the ride cushy, it'll just take the edge off and soak up the big hits. If you set it so the low-frequency stuff is damped and smooth, you're going to smack the end of the travel hard on any kind of medium sized bump. Same goes for long travel suspension. If you set it to soak up all the little stuff, it's going to start packing up on you, and you're gonna be hurting when a big hit does come. Either way, it's not a cure-all. Being a newbie, you're not going to be hitting trails hard enough for long travel anyway, so I'd save the weight and go with a shorter-travel XC specific bike.
If foot slippage is going to be a concern, look into some sort of pedal system. I use Times, I like the wider float and release. I've used Shimanos and similar, and they're good, but tight and tend to release early. Also need cycling shoes for that, which aren't cheap. You can still buy PowerGrips, I used them quite a bit, and they work well. Cheap, too. Just a simple diagonal strap you stick your shoe in and twist your foot to riding position. That will keep you from falling off the pedal better than any full suspension, and they do release fine if you fall.