I have a simple question about Heroes 5 version available here on GoG. Although I don't have plans to buy the English version (because I own the original DVDs with Polish version), but I will ask anyway.

It includes Hammers of Fate and Tribes of the East, but is "vanilla" Heroes 5 the Collector's Edition? Contents of CE varied by country, but In Poland, the game came inside a treasure chest with map, artbook, creature tables, three additional single-player scenarios, a "Special Hero Trail" option available in the game and a bonus CD with Heroes 3 (RoE only).

On GoG, Heroes 3 is available as a separate product (in Complete version). Heroes 5 has the map, artbook and creature tables in extras, but what about in-game content (3 additional scenarios and hero trail)? Are they included? If this is the Collector's edition, then it should be.

The hero trail is indeed in the game. As for the extra scenarios, I have no idea as I don't know what they are or where they're supposed to be found.

Does GoG version comes with three seperate exe files (one for original, second for HoF, third for TotE), just like my version with expansions bought separately? I think yes.

Launch the "vanilla" Heroes 5, select one player, and Custom Game. Uncheck "show multiplayer maps" (if checked) and tell me how many scenarios are available. In Collector's Edition, it should be nine. Regular version had six.

Yes, there are three different files to start the game and its two expansions, and there are indeed nine custom game scenarios available.

Dumb question, maybe, but it is very important for me: does this edition require Internet connection to play campaigns?
I have not bought this game so far because I do not support Internet validation for Single-player content in any form (DRM, activation, features, etc).

Unlike Heroes 6, no. Heroes 5 does not require any of these things. There is no DRM, no activation limit, no additional online-only features.

Oh, thank you for the answer.