You might be on to something here.
I have noticed in any thread where the topic of bow thrusters comes up there is a lot of negative comment. There seems to be some sort of "Real sailors don't do bow thrusters" mentality. There was a thread a while back asking about the topic and the poster was promptly acussed of being handicapped. Turns out he had suffered a stroke and had difficulty with brute force docking manouvers, prompting apologies all around.
I can understand your reluctance to toss a couple of grand or more at the chandler then the same again at the boat yard just to have two ruddy big holes poked in your hull, and extra batteries, and wires the size of a horses' leg, and finding out the thing is drawing way too much current because it is the home of an entire colony of a particularly tenacious marine growth.
I can also see a few problems with the trolling motor approach but most of them centered around what to do with the thing when you are not actually using it, and in the case of my boat, where to mount the thing, my foredeck being crowded already.
I am getting the feeling you are not talking about a 40+ footer, that would be just silly, and you don't sound silly.
The idea of using a tractor type of propulsion for sliding into the slip is interesting as opposed to the usual pusher arrangment. Look what they are doing with Tug boats lately. Docking with the conventional system wherein directional control astern is is only available with a little too much sternway (unless you count propwalk which almost always seems to be in the wrong direction for the space and approach available) always seems to me to be like trying to perfect an art with enormous handicaps. I do watch openmouthed when I see it done sweetly but my blood pressure always goes up a bit when I see a pannel of judges on the dock during my approach.
I say go for it. There are a few complexities all right, but if it was done well it could be really slick. I imagine a neat clean bracket that fits up under the anchor rollers. If you have a self bailing anchor locker you could even separate the 'head' of the unit from the shaft/drive assy. and have everything but the drive swivel 90 deg. and retract into the locker alongside the hull out of the way. With 360 degree swiveling you could use it to get quite fancy in your manouvering, if there was't too much wind or current, and used merely as a thruster I'm sure that 100 lbs. of thrust would do a lot of good. I would be surprised if many people could pull more than 50 lbs. horizontally.
Incidentally, I believe that the thrust they are referring to in the specs you gave the address for is measured in pounds, not in foot pounds. Thrust measuments are simply push (or pull) and are measured in pounds, ounces, grams, kilograms, tonnes etc. Foot pounds (newton/meters etc.) are measures of thrust at a distance from center, ie. torque or twist. Horsepower is a measure of torque times revolutions over a unit of time which is, in it's pure form, the ability to achieve a certain amount of work in a certain amount of time. Crossing thrust over to HP. is fairly complex since there are so many variables such as the medium you are thrusting in, the efficiency of the machine (prop, jetdrive, wheel etc.) there are tables but they are only approx. It would be better to compare by power consumed or watts, (volts X amps). Watts are directly transferrable to HP. 1 HP = 745.6999 Watts.
Let us know how you do, this does have possibilities if done well.
fair thrusting to ya'