Your dealer advised you well: Varget is a great powder for 22-250, so is H380, and RL-15. There are others too.
RugerGP100fan, with 20 cases I suggest you simply load them to the same COAL as factory ammo. When you've figured out the length of your chamber, you can then start seating the bullets out closer to the rifling, and see whether that improves your groups. Watch out for pressure spikes as you move the bullet out closer to the lands. Keep good notes.
Since in the long run you will probably end up buying regular Large Rifle Primers rather than spending money on the Benchrest ones, there is not much point in working up a load with the BR2s. You will only have to start over again with the regular ones.
Use the BRs up as you become familiar with your equipment, and learn what happens to a case as it is repeatedly fired and re-sized, etc. It is important to keep track of the life cycle of your cases, and to keep them sorted according to the number of times reloaded.
RugerGP, please do not take offence at this ... you barely have enough empty cases to properly and systematically work up a load. You ought to purchase a 100ct. bag of 222-250 brass.
If you don't have one, get a reloading manual and read it carefully several times. Then check back here and we will all be glad to help.
Have fun.