I've been using SLM since 2012 and have loved it (Thanks!). I love that you can now modify layout views to your liking, although I'd suggest having something like "List Only Classic" so it would be less of a shock to people upgrading (just a thought).
How would "List Only Classic" differ from the existing "List Only" layout? I tried to match the most popular layouts in version 3 with the default layouts in version 4. The problem is that even in the old version, there were so many different layout options that it was difficult to capture all the possibilities. But since the layouts are all customizable now, in theory you should be able to get exactly what you want, perhaps with some tweaking. This is why I've been recommending not installing the app right before a gig, in case you need to make some adjustments to get your preferred workflow.
1) In the song layout, you can swipe horizontally to change songs. This gesture isn't available when viewing a full-screen document. I should be able to restore that in the next update.
2) Can you post a screen shot?
3) I'll add this to my wish list.
4) A double-tap will auto-zoom a document. I've never seen a case of a single-tap doing that. A single-tap on the right third of a document should show the next document, if multiple documents are attached to the song, or do nothing if this is the only document attached to the song.
5) Tapping the right hotspot to move between attached documents (or lyrics) is intentional. Having to go back through all the previous selections is a bug and will be fixed in the next update. I think this problem only occurs in the Songs list, not in the show view.
6) I haven't seen these problems and nothing here sounds like it's related to the themes. The speed of opening the show view is more likely related to the number of recordings on your device, although the longest I've seen is about 10 seconds, not 3-4 minutes. If that persists, please contact me directly and I'll give you instructions for capturing and sending a console log. To change layouts, you do have to be in the show view with a song selected.