using the big motor for the tl sounds good. The wiper should be fine for seat moving. I use a wiper for my tl too and it works really well. But more power should give you some reserve for more motion of the tl. I only use 15cm+15cm (feft /right) at the moment.
Perhaps you know my thread? If not please compare our both designs. I use a distance between the front bearing and the seat. This inertia (in the seat) while rotation gives the immersion in my opinion. I don't think you will feel a lot with your planed design. You sit on top of the bearing - in a real car the rear axis "rotates around the front wheels" when traction is lost. I would use the bearing where you expect the front wheels in your simulator. Of course you would need a second bearing in the rear...
BUT this are just my thoughts and we are discussing here
edit: added link to my traction loss topic: http://www.x-sim.de/forum/viewtopic.php?f=37&t=289&start=60
.. + some deatiled video on page 8
@ all --> I think it would be generally very loyal to post his projects only in the forum where you use the software from ... but of course everyone is free to do what he believes to be right. no criticism