does purchase include future updates or is it just up to 4.xx and then ill have to buy 5.xx, and so on?
Unfortunately, yes, access to each major version is purchased separately. Currently, purchasing on itch.io is equivalent to a monthly subscription on Patreon/Boosty/Subscribestar and primarily serves to support the developer, as after some time (when the next major patch is released), this version will become public.
We will change this approach to a one-time purchase when we get closer to the release and decide that the game is practically ready.