>>15884274
It's been a long time since I've last played through Homm 2/3, but the optimum strategy is typically to hire the maximum number of heroes, (except for perhaps small maps). You'd always hire the 2nd hero right away, and the rest on an as needed basis.
Some of those heroes will actually fight and earn XP, while the others are purely for transport and re-visiting spots on the map that refresh every week (windmills, dwellings, etc.). Once you've found enough windmills and such in your territory, you are going to need at least one hero dedicated to plundering them in an endless, non-stop loop. Like, even if it takes 5 days to complete the loop, that hero can't really do anything useful with 2 free days so consider him dedicated to the task.
On easy/small maps you can get away with having one super hero and the rest be useless guys for transport and random activity. But one super hero is not normal. Normally you should have at least 2 heroes that get experience. The more powerful one will eventually be offensive, while the other is only defensive. 2+ offensive heroes is common too, it just a matter if the map size is large enough. The AI always knows if you've left your mines and castles without strong heroes "nearby", which is why you need a defensive hero with good XP. The defensive hero can sometimes invade as well once you've broken the enemy's back and are just doing mop up operations.