Could clear one question - what about future game updates? Could they be applied to your version of the game?

GOG always offers updates for the games here. So I don't know why not. :)

Given that on the game page it clearly says "free content updates" I would think so, just when the next update drops(1.3 I believe) it should come here(it may drop a little later due to how GOG handles updates) but if you mean if you can take the Steam patch and apply to the GOG version..nope.

the thing is that I'm absolutely new on GoG and haven't bought any game here, so that's why is the question. I don't see any mentions about "free content updates" on the game page - http://prntscr.com/4scr2b

you really should learn to look

Most developers honor and support the GOG version of their games, remember is the dev not gog that supplies updates for the most part especially in the case of indie games. It will probably be at least a day or two after the steam version gets the 1.3 update.

GoG likes to test updates to make sure they dont render the games they sell unplayable, so GoG can be a little slower then Steam.

Or 3-4 days when it's during the week-end ;)