If you are using left winger feathers which way should the bow string and serving be twisted?

Makes no difference. The two are unrelated.

It is a good idea to twist the serving and the bow string in the same direction, so as you add more twists to the bowstring, it tightens the serving rather than loosens it.

Right wing or left wing doesn't mater but serving should be wrapped one way for a left handed shooter and the opposite for right handed .

Which way should the serving be wrapped for a right hand shooter?

IMO, the way the serving is wrapped makes no difference at all as long as it's wrapped tightly/correctly.  I've been making strings for more than 30 years, and have wrapped from both ends and have never had a serving unravel.

Endless loop strings generally aren't twisted.  Which way is one suppose to lay the serving on an endless loop string?  Yeah, I know, some are twisted a bit to get the correct brace height (after they're served).

With a flemish twist string, a right handed string maker will twist the string in the opposite direction than will a left handed string maker. I suppose one could twist on the serving in the same direction as the direction of twist, but who's to say it wouldn't work just as well, and maybe better, if one twisted on the serving opposite the string twist direction.

I bet 95% or more of commercial string makers (whether they're right or left handed) start the serving at the top and wind toward the lower limb.  I don't know of any string maker who asks whether the buyer is a right handed or left handed shooter before he makes/serves the string.  He asks for the bow length and/or what length the string should be made. 

Don't overthink this stuff. 

Thanks everyone for the responses.