If you do decide to try something in the bulldozer family, try a set of these tank motor and drives, they are not that expensive.
http://www.ebay.com/itm/Upgrade-Stee...item5ae34458a8
Then maybe add an old Tonka T-9 dozer, would get you a start and keep you in the hobby.
http://www.ebay.com/itm/TONKA-Mighty...item1e68494e68
More fun to learn and try then to sit back and read topics, just my opinion.