Ok, so here's the deal generally speaking in these situations, and I would imagine the situation with this game won't be any different from Being A DIK / City of Broken Dreamers, etc...but I could be wrong since Ocean can do this however he wants, so just keep an open mind and pay attention with Ocean's dev logs in case things change.
I'd personally recommend NOT buying the Steam copy right away if you want to become a Patreon member - you will not automatically become a Patreon if you buy the Steam copy, you're just a person who bought "Season 1" on Steam. What Ocean will "probably" do is when the game launches on Steam, the game will include Chapters 1-5. And then Steam probably won't get an update until the next set of 5 chapters releases - that's how Being A DIK / City of Broken Dreamers, etc. does it.
You just kinda have to decide what you want to do - if you sign up on Patreon, you'll pay a monthly fee, and depending on that fee, you'll get access to certain things (Dev logs, game releases, etc.). (you can cancel this at any time also, just fyi - just be advised you get charged at the beginning of the month, and if you cancel your subscription you lose all access immediately no matter where you are in the month, so if you cancel, cancel at the end of the month on the last day or two)
What I do is back on Patreon just to support the development of the game but I usually download the updates here on F95. I don't back to a high enough level to get the game on launch day - for example the recent Beta required you to be at the $22 per month tier to get it on launch day which I think is asking a bit much, so I just waited a few hours and it popped up here on F95.
So my advice would be: back to the $ amount per month on Patreon that you want to support Ocean with, and then just pickup the updates here on F95 and then add the game to your Steam launcher. I add all games to Steam launcher so I have them all in one place with a custom background and everything for the game to make it look more official, so you can still sort of "have it on Steam" if you want.