I can not emphasize enough that old RM way to make monsters is miles above new suggested way.   Hits, DB, OB, movement and some monster /animal skills should not be related to level. Old prime excemple was T-Rex - no need to say more. Some monsters have profession and thus level is somewhat meaningful but e.g. vampire is primarly vampire and not some archetype like subterfuge semi spelluser. Beta monsters were broken in many cases.

I think that the biggest problem arises from use of single level for all aspects. For monster I'd use at least two levels: RR&spell level and skill level. Actually I'd use additional combat level IF level was neccessary for combat  (it is not).

Biology or what ever reason that gives some ability differs so greatly that all monsters shold not be shoehorned in same model.
E.g. for combat there is wide spectrum how the ability arises e.g. for elemental attacs : unintelligent fire elemantal's elemental attacs accuracy, potency... arises from very different source than fire giants or orc mages abilitys to throw bolts .

While playing RM2 or RMSS I sometimes do wish that there were information about important skills like perception, tracking, stalking but most monsters are good with just RR-level.

Combining all in one level is mistake. Even D&D uses dice and challence rating.

I'll buy all moster books ICE publishes but will I use them? 

I don't think Underground Races changed the Common Orc or Greater Orc stats from how they appeared in the RMSR or in RMFRP Character Law. So if you are just looking for the stats, you don't need it. However it does add Scrug, Vard, and Grey Orcs, plus lots of background material and other character options (talents, training packages, etc), so if you want to assess whether the cultural information there can be adapted for your purposes, that would be something to look at. I don't know WoW well enough to answer whether it is close enough to be useful.

Done.

Thanks 🙏🏼🍀

This is how we calculate Total Hits.  I think it is fairly close to RAW, and if it isn't, it's how our RAW is set

Total Concussion Hits = Base Hits [CO/10 rounded up + hits rolled per rank (up to racial maximum)] * (1+CO Bonus/100) + (ProfLevelBonus * Ranks)

Example: 4th level Dwarven Fighter with 90 CO (+25 bonus) and 10 ranks in Body Development (with an average of 6 rolled per rank), would have: 90/100 (9) + 6*10 (60) => 69 Base Hits, 69 * (1 + 25/100) = 86.25 rounds down to 86  + 3*4 (12) => 98 total hits.

Example 2: Same Dwarven Fighter at 10th level and 22 ranks in Body Development (with an average of 6 rolled per rank), would have: 90/100 (9) + 6*22 (132) => 141 Base Hits (over max racial, so capped at 120), 120 * (1 + 25/100) = 150  + 3*22 (66) => 216 total hits.