Interesting point. Are we expecting B-1 pilots to go through training first? Don't they mostly need systems and stealth tactics training? Or perhaps it's 50% new guys. In a two crew configuration don't you stick a new pilot with an experienced B-1 pilot? Why wouldn't you use combat coded aircraft?
If the B-2 is a guide the Raider will be a two pilot operation, WSO's need not apply. Don't feel too bad for them, there are all those empty F-15EX back seats... A few of the younger ones will get routed to UPT and come back as pilots.
The whole time I was around bombers the B-2 was a board only selection, since it always was a small community of priceless national assets, things may have changed since then. The best example of a largish transition was the Bone in the late 80's early 90's, all of my leadership in the early 2000's was that initial cadre. The initial cadre and first few batches of aircrew were all board selected. Once the community had a critical mass then it went to a more normal model of an FTU with short (other airframes) and long (UPT grads) courses.
So, initial Raider cadre will likely be board selected B-1/B-2/B-52 pilots with a few F-15E/F-35 guys sprinkled in, all will be super high potential folks. Price of entry will be IP on their respective type, O-4 and above will be top heavy on gray patch wearers. That will stand up the FTU, first combat coded squadrons' IOC's/FOC's and the weapons school. After that it all comes down to how big the fleet gets. Hopefully, the buy makes it to 130-150 jets in 8-10 combat coded squadrons and the pipeline gets set up to provide the right number of IP's and weapons school grads to become self sustaining before UPT grads start showing up to the FTU.
All that to say, the guys up at the 28th BW are going to be board selected for a while, the Bone pilots not selected will get to go south, get a staff job or transition to other airframes short on pilots/WSO's. The first batch at the 7th BW will be the the high potential types, at some point along the way they'll move away from the board and a flesh peddler at AFPC will figure out who transitions, who goes elsewhere and when to let the UPT guys put the Raider on their dream sheets.
So, hopefully this answers your question about experience. Most if not all of the initial cadre will be highly experience IP's on some other airframe and will train to be the trainers, with heavy input from the contractor and test community.
Unless Northrup pulls an F-22 situation where early blocks are not fully combat capable, then there will be no "combat coded aircraft" only an aircraft allocation for a combat coded squadron. When I was in the Bone community our jets were for the most part homogeneous, with a few notable exceptions. Pretty much every jet on the ramp was the same configuration, except for the one or two test jets with something in OT. When we got a tasking for the combat coded squadron (the 9th) we picked the best 8-12 jets on the ramp, regardless of if they had a 9th or 28th tail flash. The 12 PAA, means that the squadron will be expected to provide up to that many for a combat tasking, hence you probably have 14 jets, one in phase and maybe another sometimes at depot, but if there's another squadron on the base the expectation is that you'll use theirs as well to meet the tasking, else you may need 15-16 to meet the 12 if the airframe has a bad rep for reliability. Biggest consideration there was the number of hours left till the phase inspection. Doesn't make any sense to send something down range with less than XX% of its hours left if you're just going to have to swap it out in a few weeks.
All this to say, take it with a big grain of salt, it's been a while since I left the community and who knows what new idea(s) they've discovered since then, but it should give you the flavor.