Steam and RGL compatibility (Red Dead Redemption 2)

I own the game in RGL since the time of open pre-orders, I took Ultimate Edition with burning eyes without thinking. For some reason I am thinking about taking the game, only already in Steam for greater convenience in the form of screenshots, statistics, etc. Only a couple of obvious questions arise before me:
- If I buy a version in Steam, will I in fact own two copies of the game, or will it merge into one (Steam) version?
- If I buy the version on Steam, will all my story / online progress from the RGL version just be transferred to the Steam copy?
- If I own the maximum edition in RGL, then will I have to buy a standard Steam copy, or will they fork out for Ultimate again? How could this affect the game when buying the default version? Various ultimate bonuses in the form of a Thoroughbred Horse, Volcanic Pistol, etc. would disappear. etc.?