The first place I'd recommend to see if there are similar conversions to use as guides is DIYElectricCar forums, and/or EVAlbum. Small car conversions will also be useful references.
The main complications are mechanical, in making the shaft adapter(s) and the adapter plates for mounting the motor to the existing transmission if you want to keep whatever gearing is there. If you don't, then you make the shaft adapter to fit the transaxle input. Depending on the motor speed, you may need a reduction gearbox between those.
Alternately you can use hubmotors in the wheels.
Places like QSmotor and GoldenMotor and probably many others sell car wheel replacments that have the motors built in. They're brushless, so the controllers can be a little more complex but ti's more efficient and almost as easy to hook up.
Batteries...you can use lead acid, (SLA or FLA) but they are very inefficient, heavy, don't last very long for the cost, etc. Lithium batteries probably won't cost that much more, and can last many times longer and either weigh far less or give you many times the range / capability for the same weight. You can find used Nissan Leaf packs that are designed for large EV use relatively cheap, and probably others (the Leaf are just a nice easy to connect format).
