A THREAD FOR NEWCOMERS!

Another question. What maps do you play online – size, presence of years, monster strength, difficulty.

If you mean fixed maps, go to the Heroes3 online section – online tournaments for Heroes 3, there you'll find Seasons of Year – a seasonal tournament on fixed maps, and you can see which maps are used in which season. If you mean generated maps, then they are definitely played without water, 100%, monsters are strong, there are 2 players, everything else is set to zero:), size L (Large) + U (underground), time 2, 4, or 6 minutes, whatever you prefer.
IMHO – I Have My Opinion, Hard to Dispute :) at least that's how it was explained to me, maybe there are other options:)

If you choose a castle, is there no hero?

Well, if you play according to the seasonal rules, then when playing as Conflux, the starting hero is random. And in general, read the seasonal rules – everything is explained in detail there, and how to choose a castle, and so on.