OFB-11!

Is it possible to choose Gosha and a starting hero for the Conflux?

Yes, it is. Even Isra and Vidomina. There are no restrictions on leveling.

Does this also apply to anarchy?

Rebuilding is enabled on all templates and on anarchy as well. To do this, you need to play with the ХВ-rules module enabled, but uncheck "ХВ-rules" in the options. It needs to be updated during restarts. Besides rebuilding, this will also give 2500 gold at the start (if playing at 200%), which slightly reduces some risks. In our case, it's played at 160%.

Can someone explain clearly what this is related to? Why is gameplay with three castles so bad?

This dates back to the times when all-random was played on anarchy. When playing with random castles, a discrepancy arises between starting towns, heroes, and native land. For example, you could have Rampart on a swamp with a starting necromancer — that's completely unplayable. With manual castle selection, there is no such problem: three native castles and a native hero. However, the habit of banning such schemes by agreement has remained. I personally don't play them either.

I'm also interested in the question about rebuilding on anarchy. After all, anarchy is like true SoD with key-holder tents; should rebuilding be enabled?

Well, if there's a painless option to enable rebuilding, why not use it? :rolleyes:

P.S.: I also remind you that on anarchy there is no such concept as restarts upon meeting or upon blocking. Therefore, I recommend discussing this point with your opponent before the game and adding such options by mutual consent.