You do not necessarily need PC. IMHO, it makes it too strong. I don't know what it means to have late stage proteolysis or late stage appearance. Maybe aminopeptidolysis, but you don't get that with PC usually. Usually, that happens due to synergistic combinations of yeast and b linens or yeasts together, and sometimes geo. For reb, I would do a yeast that is moderately proteolytic, a b linens that is moderately proteolytic, and a geo that interacts with it (hopefully this is in a large cave and there are multiple geos). PC can sometimes show up in a cave, but typically doesn't for reb.
Or, slurry the rind and do that. It's somewhat tricky to do on a small scale.
the gradient is a property of reb due to the affinage. You have high MFFB in the wheel, then you put it on those old boards, and it loses water at 85-90 RH (or maybe a bit higher, have to balance water loss and maturation rate. You don't want b linens running wild, though). And in the meatime, it will go through the typical progression of growing geo, and then b linens/reblochonii. So the enzyme action breaks it down, all the while it's losing water, creating this effect. Can help it along by brining in saturated brine to create a moisture gradient. It's tricky, though because you need a good surface Aw level to encourage the right blend and succession.