I’ve been using an R2 Pro for ten months. Very early on I looked at the specs and divided 2300 watts by 14 power levels. I then did the same for an R1 which has 9 power levels and a max of 1500 watts. The watts per step are virtually identical for the R1 and R2 Pro which tells me that any recipes for an R1 will work on an R2 Pro with no changes needed. Power levels 10-14 do not exist on an R1, so any R2 Pro recipe that uses those will not work on an R1. But you can use any R1 recipe and expect it to work on your machine.
From other posts by some of the experienced Bullet roasters on this forum, I have determined that there is no definite formula for converting a recipe to smaller or larger batch sizes. As for roasting in general, you can look at posts by folks like Babs or bradm or blacklabs and get some really good info about roasting as well as some recipes that they actually used. They will discuss things such as charge temperatures, heat levels, fan speeds, etc., and you will have some very good knowledge with which to work.