> When I fold the tracks over on themselves, do I need to glue them?
It's not necessary but with some glue inside You can get little bit more massive tracks.
> There are 4 lengths of tracks supplied with the model, 2 for each side. How do you join one length to the other?
These tracks are spare tracks (or You can add these to a lenghth when You need).
How to do this? I can recommend small pieces of plastic over the folded track and to hide this construction under the wheels.
Sincerely Alexey.
http://www.acemodel.com.ua