1. yes, eventually the female characters and straight stuff will get added, but it's not a priority since Hyao is focusing mainly on the new stuff being added. eventually he is going to get all the old stuff in the backlog finished in either one major backlog update or throughout a couple different smaller updates with less new stuff and backlog content instead of just a big/regular content update.
2. not as far as we know. there will be CGs for other characters and routes like Bottom Logan, but none of it will be animated. maybe this can change but I don't believe Hyao has said anything about it changing from CG to animated stuff.
3. sorta? we learn some new stuff about Mythshore's past soon but nothing for its main story is getting updated.
4. yes. it's kinda already started to shape up that way, you have the Bottom Logan route for example and corrupted Lizard tribe. growing stronger than the nameless is a little bit of a stretch but could potentially happen. being eviler than him is also a weird thing since we don't know if he is ACTUALLY an evil person, we just know he is willing to do anything for his goal. whatever that goal is.
the warrior of purity thing though is both possible and incredibly unlikely. it's unlikely in the way you described it, but possible. however, it's more likely for specific characters instead of as an entire route, like the scene if you're a virgin with Logan's werewolf attack against the invading swamp monster.