Not yet, but he said that since Patreon took him off and that was the reason he was holding back originally, Chinami and Tsukasa will be lewdable in the base game (optionally) in the future.
There was a loli uncensor patch a long time ago that removed Tsukasa's towel in the onsen, but the link to it no longer works, so I don't know what he's talking about.
Not really. Early on it's pretty nonlinear, and so the "optimal order" is just "make sure you do Rin's events early because a lot of Main Events are gated behind her affection 15 and 20 events," but then later on stuff becomes more linear where you can't do a given patch's content until you do the previous patch's content. There's a link to the Wiki built in to the game and it's good: if you're ever stuck and nothing is triggering, just look at your Main Events list, find the first event you haven't done, and look up the requirements for that on the wiki.
But, uh, the point of the game is the words and story. Not the H scenes. If you're viewing the words as an obstacle to pass to get to the H, save your time and play something else.