Multiple questions about relations / routes

I'm trying to learn how to properly create relations for MTB way routes and have the following questions:

1. Is it possible to create a relation route by just designating the relation for a subset of way segment nodes instead of entire way segments? This would allow route creation without having to split ways into segments at all intersections where the route turns onto a new way. There would be no direction to the route but that is not a problem for the routes I want to create (they can be ridden either direction).
2. (Assuming routes must consist of way segments with direction specified correctly), how do you handle a single route that passes over the same way segment twice but in opposite directions?
3. Related to 2., how do you handle multiple routes that use the same way segment but in opposite directions? I have read that you can duplicate the way segment so you have two spatially identical way segments "on top of each other" but with opposite directions. Is that the correct way to do this? I worry that subsequent tag or other edits to the "top" way segment might miss the duplicate "bottom" segment. Also whether that would foul up name rendering if there are two identical segments with the same name rendered twice.
4. Are there any detailed tutorials / info sources explaining how to create relations to designate routes for ways? Please reference if so.

Thanks for the assistance.