SFO makes a lot of changes that ultimately end up making a lot of changes for the sake of having lots of changes. Most of the systems still work functionally the same, you just now have to find a different way to break them, or the changes amount to a lot of plugging one leak in one area only to create another in a different spot.
It's good if you want a change of pace, but I wouldn't play SFO because it's somehow 'superior' to vanilla. It's not. It's just a new way to play, which is nice if you've put in 500 hours or something and want to try something new.>>277220
As for more units, here's what I run to get pretty much everything I could ever want.
Boyz will be boyz-more greenskins
Expanded roster full collection-adds new units to basically all races, more always on the way, use the compatibility patch with boyz otherwise you get dupe units but nothing broken. This is your massive unit pack, almost all of them are lore friendly or lore friendly adjacent and they are generally of very high quality. I suggest just getting the whole thing.
OvN Lost Factions-for new factions and some new units for existing factions in a couple spots. Works very well with expanded roster.
Regiments of Renown Compilation-exactly what it says, more RoRs for every race.
Cut Content RoRs-adds back some cut content RoRs some anon found for skaven and high elves. They had actual game files but never made it to release, so they're generally high quality if a little iffy on lore in a couple spots.
Sam's Ghorgon-self explanatory
If you include heroes in that list of units you want more of;
Mixu's TT Lords and Heroes mods-anything by Mixu is generally very high quality, can't go wrong
Mixu's Mousillon-full roster, including RoRs and LLs, for Mousillon as a new vamp count faction with Mallobaude
If you liked Vermintide, you can get a mod for all 5 of those guys as Empire heroes, although this is a little unbalanced since they are all really good.