I'll use the word "update" for what you call "patch":
1. 0.7.5 ends the same regardless of your choices. Though what happens right after, in the next update, might depend on your past decisions.
2. Most of your saves should work in the new update too, yes. It hasn't been 100% reliable in the past though, so please keep at least a few of them if you want to purge some.
3. There is no update schedule, instead the dev has a "progress bar" that he updates every 1-2 weeks. Only when nearly done, the update release dates for all the different crowdfunding tiers are announced. When looking at the rate of progress so far, a winter release seems most likely, yes.
4. The current update is 0.7. The dev himself isn't sure about the exact number of updates, though he estimates that it might end somewhere between 0.12 and 0.15. Time between updates has been ~6 months with a rising trend. So yeah, we're still talking years here.
With your level of enthusiasm you'd fit in well on the Discord server, yes :) Though because of spam problems in the past, only crowdfunding supporters or ex-crowdfunding supporters can write any messages there.