Nick, if you think that Accurail cars are difficult, you might be better off building your skills a little more gradually than jumping into trying a craftsman-type kit. I would put Accurail right up there with Athearn for ease of assembly: no working doors to contend with, no separate underframe, except on the singlesheathed boxcars, and even then, it's only two snap-in pieces. The brake gear is three simple castings, plus a brakewheel (Same as Athearn). I'd rank Athearn, MDC/Roundhouse, Accurail, Bowser, and Walthers all as shake-the-box kits: some have a few more parts, but they all are pretty basic if you follow the diagrams. If you want to move up the difficulty scale, the Proto1000/2000 kits might be a good place to start. Again, everything is supplied, you don't have to fabricate anything. There are more parts, to be sure, but the most difficult comes in handling the slippery plastic grabirons (oversize, by the way) and removing the one-piece brake rigging from the sprue is a bit tedious. Once you progress beyond shake-the-box kits, you'll also need to expand your toolbox: besides the obligatory Xacto knife, and plenty of sharp blades, you'll need small screwdrivers, at least one pair of good tweezers, and a few styles of needle files. I'm told that sprue cutters are very useful for removing delicate parts from the casting sprue. A pin vise and a set of modeller's drills can also be very useful. Similar to the Proto kits, Intermountain, Red Caboose, and in some ways, Tichy would be your next step up the skill ladder. These three offer still more parts, with some options as to which should be used, such as different door styles or brakewheels, etc. The Tichy kits are the only ones, so far discussed, to offer metal grabirons, and for this, you need to drill the appropriate holes. Ditto for the brake gear, and you also need to construct the piping and rigging from wire, supplied with the kit. After this, you're into the realm of craftsman kits. Westerfield, F&C, Sunshine, and Sylvan, and countless smaller outfits come to mind. While many of these manufacturers are now offering one-piece body castings, most of these kits include a bunch of small parts, plus a bunch of material from which you're expected to create the rest of the detail. Instruction sheets can run to several pages, and often trucks are not supplied. Most of these kits are of models of prototypes which were not as common as those offered by the manufacturers listed previously. Older craftsman kits, many still available, came with two sides, two ends, a multiple-piece roof and a separate floor, plus all of the parts for the modeller to build the underframe. Often, the sides would be of slightly different lengths, or the floor width would require adjustment in order for everything to fit together properly. None of this is particularly difficult, but it does take more time and requires you to learn more skills, all part of the enjoyment of model railroading, in my opinion. Once you've assembled the car, you'll need to paint and letter it: more new skills and more new tools required.
I'm not trying to make light of the difficulty that you may have assembling kits "beyond" Athearn BB, nor am I trying to dicourage you from trying a craftsman kit, but there is a learning curve here, and you can progress through it only if you want to. We all started out simple, and there's nothing wrong with keeping it simple if that works for you. On the other hand, if you push yourself, in measured increments, you'll gain new skills and new confidence in your abilities. In my opinion, this is good not only for your model railroading, but also for you personally. The key to success in this endeavor is patience. The skills will follow.
And while I'm one of those "retired guys" refered to earlier, I only wish that I had the money to be able to afford more of those craftsman kits. While I've probably got way too many freight cars already, I still enjoy picking up stuff from the used table at the LHS, and fixing it up with added details and new paint and lettering. This is also an affordable way for you to move beyond "shake-the-box", and learn some of those new skills.
Wayne