Just put a link in the description
Basically. But there is also dedicated places you can put links. Just look at some game descriptions. And open the info box of the game. You might find a steam, patreon and other links there. And maybe a wishlist us on steam appeal in the description.
Also many have links to their discord to chat with players.
The thing is, itch is a platform where you can put your unfinished game and even sell it. Players will of course expect you to release the game here, if you sell early access here. That is one of those promise one thing, deliver another. Some games that sell here even give out a steam key.
For pricing just look at other games. There are several options to put out a free demo with a purchaseable version together.
What worries me, is that you are not even sure if you want to finish the game and would want to base the decision on player feedback. Your feedback is gonna be biased heavily. People hating it and people loving it will be more inclined to express their feelings. But even if you get more hate than love, it does not say much about future number of sales, as most people will just not comment or even rate the game.