It is release announcement. Not announcement of the beginning of development. Posting there to talk about a game that cannot be downloaded is a non sequitur.
Itch has no regional pricing.
You can put your finished Steam game here and give a Steam key with the purchase, if you like. Use the US price.
You can make a blog posting (a devlog). But if you do not direct people to it, there will not be much discussion there. You have no followers on that account, so no one will get informed about that blog posting. Except people looking at the global feed at that time or finding the post by internet search.
If you have a working prototype, set your project up as usual and disable payments. It is a prototype. That is even less than a demo version. If you get paid, and would upgrade that project, all customers would get the release version. If know what the early access price should be, you can set the price (and designate the old prototype as a demo version on the same page). You will get more feedback and comments on your game page than global itch community. Individual results may vary, but that is how I perceive it. But you can try the feedback section as no time said. If you ask specific things, people might be more inclined to answer.
Edit. I might have misunderstood. But your mentioning of prototype was making me think you are working on your second game. If you are releasing your first game, just set the early access price the same as the US version of Steam and decide if you want to give a Steam key or not. The benefit of Itch versions usually is, that they are drm free, so not everyone is doing this. Otherwise all of the above also applies. If you set no price, no one can buy, but still download your demo versions and talk and rate and follow. Once you go to buyable early access, you can set the same price here and regularly sell, as per default all games on Itch are "early access", unless specified otherwise (the released and in development states of games are not to be trusted. Some people "release" their in development, and some released games do not switch from in development to released once they are done.)
Clarification: no price is not the same as pay what you want with 0 minimum price. Paying 1 $ gives ownership of the project for all future price changes of the minimum price.