For stats, see the books. It is fairly significant to figure out whether you are using RMSS/RMFRP or RM2/RMC. RMSS and RMFRP are close enough you can borrow back and forth with no real issues, but are different enough from RM2/RMC that going across that divide is more awkward.
RMSS core book includes: common men, mixed men, high men, wood elves, grey elves, high elves, half-elves, dwarves, halflings, common orcs, greater orcs, half-orcs
RMFRP core book includes: common men, high men, wood elves, dwarves, halflings
RMFRP's Character Law adds: common orcs, greater orcs, grey elves, half-elves, half-orcs, high elves, hillmen, mariners, nomads, urbanmen, woodmen
Not enough?
RMFRP's Races & Cultures includes: centaurs (horse, lion, lizard), droloi, dwarves, elves (wood, grey, high, dyari, erlini, linaeri, loari, shuluri), fey (dwelfs, satyrs, tylweth teg, lennai), garks, gnomes, goblinoids (goblins, hobgoblins, kobolds, murlogi), gratar (black, green, grey, yellow), half-elves (eritari, ky'taari, punkari, sulini, vorloi), halflings, half-orcs, hira'razhir/hirazi, idivya, jhordi, men (common, high, mixed, laan, umli), mermen, orcs (common, greater, lesser lugroki, greater lugroki), quishadi, shuikmar, sohleugir, saurkur, troglodytes, urlocs, vulfen
There was also an Underground Races book for RMSS.
For RM2, there are a ton of races in the various Companions. Not sure what is available in RMC.