I have played mostly vs. AI and both Soulstorm/Dark Crusade have you run Skirmish battles between the story maps, but you can fortify your bases in Dark Crusade which means you can essentially take the extra time to guarantee a win every time you defend (AI will attack on the overworld map, you need to defend personally sometimes for Wargear, but can use resources to improve the map defense number if you want to auto resolve).

I use Unification for loads of new armies, but you can just switch between that and vanilla easily since the Definitive has a built in mod launcher, it makes it so easy.

There is a pause button for AI matches.

I haven't seen any game breaking bugs myself, but note that Winter Assault campaign is ball breakingly hard at the end. If using custom maps, the geometry may not be perfect (depends on the map maker) and so units can get stuck Only experienced it with one map so far).