One thing to keep in mind when using automotive electric motors. Many of them are pretty crudely constructed, with little thought towards efficiency. The reasons for this are that many are used for short duty cycles, as in window motors, so long term heating or efficiency is not a concern. Being able to draw very large currents from a storage battery allows for sloppy designs also. Many of them have over sized windings to help generate greater torque with less turns, resulting in massive stall currents, and often very high in-rush currents on start-up.
For example, a common Bosch window motor runs no-load around 5 Amps, but stalls at well over 30 Amps.
Wiper motors are not as bad, they are designed for more continuous use, but they do draw pretty hefty currents when loaded. One problem you may have with a wiper motor is the case being grounded to the motor, and the other connections being for speed and park return.
A wheel chair motor with the gearbox attached would be the perfect thing, not sure where you would get one though.
PS, if your questions are all about one project.... maybe they should stay in one topic? It makes it easier to follow.