Yeah, once you finish it, you get a choice to fully unlock the gallery, even the stuff that you haven't played.
To see the most content, you should go the slut route, but there will always be stuff you can't see in the first playthrough. For example, you can't complete the love route with vivian and at the same time, have her corrupted. There's no wrong choice, it's a matter of knowing what your favorite kink is and going there first.
You can't grope Vivian as far as I know but she can grope Carwyn.
The steam version is better, sadly they share similar bugs. I haven't found game breaking bugs but there are quite a few. I bought it to support the developer but the way it looks is like he just uploaded it and forgot it, just an attempt to milk it as much as possible. Which is kind of disappointing. The idea has huge potential but it's too niche, if the guy really wanted money that bad I think there are better games for him to make. I was expecting more care for the details.
Anyway, I think for 10 bucks which is the money I paid on steam to buy it, it's totally worth it.