1. Stay with the Sendaro 300 win mag until the barrel goes. RUM is too **** difficult for most people to shoot and become proficiant with.
2. Have the sendaro trigger tuned, skim bedded, luggs lapped and recrowned now. That is all that needs to be done until you rebarrel, then action job.
3. The scope you have is good, send to Premier reticles for reticle conversion to either their Gen 2 mil dot or what ever you prefer. If it does not have the target turrets on it, they can add them too.
4. Buy a leica 1200 rangefinder
5. Get quality reloading tools and start reloading if not already.
6. Start shooting either Fclass or 1k BR. You need trigger time with people who are shooting LR.
7. 40x is waste of money. needs truing 90% of time anyway. Save your $ for quality custom action
8. When getting ready to build a custom gun, do some research. Ideal is local smith that builds LR rifles and knows his business and is recognized for it. Guess what it will cost the same and in some cases less to do it right the first time. Lot of those in NE, just ask all the PA 1k shooters and look at the recommended smiths at 6mmbr.com, Bruce Baer, Mark King, Jim Borden, John Myer in VA, Clay Spencer (VA), Hammond, Wolfe etc.
Good luck
BH