Yes, you can opt for "girl on girl" scenes only. You can even complete the game without seeing any H scenes at all if you prefer to do so. Some players consider this a flaw but the decision is always up to you.
I'm in no way trying to dissuade you from getting the new version, just sharing my 3+ years of using RPG Maker series.
1) Just marketing bull or I don't get what is mentioned here. The project size is almost irrelevant. Before deploying the game you can exclude unused files, which brings down the game's weight down to about 100 MB. Most of the engine files are simple libraries and json files. For example, Yorna's Windows release is 1.58 GB with the main bulk of weight coming from 1407 pictures and 22 tracks. MZ won't reduce it in any significant way.
2) Oh, don't even start me on this. I perfectly remember how projects fatally bugged out and crashed after a minor performance update in Steam from Kadokawa. Many devs without backups lost a ton of work due to this. And speaking plainly about performance, your vacuum cleaner can run RPG Maker games, so it's yet another marketing bull. Plus, the non-existent support from Kadokawa won't allow me to invest in any of their stuff.
3 & 5) Let's just be honest. RPG Maker games aren't expected to look beautiful like the Crysis series. Animations can be done prettier, yay. Most devs will still use the default ones since they fit and don't consume your time for creation. That's the whole idea behind RPG Maker - it allows you to save a huge chunk of time on basic coding and base assets.
The ability to map layers can be useful in some cases. For example, you make a room with furniture and other details, then decide to change the floor and wall tile. In MV, doing this will erase all the furniture so you'll need to place it again. In MZ, you can map them to another layer and just change what you need. Still, a very limited use since it's easy to make a mock-up version to test out how the things will look before committing to the final version of the map.
And most of the time the extra layer won't be needed. I don't know, let's just take a popular RPG Maker game from this forum. Town of Passion popped first for me. Are all zones using enough details to fill all 3 layers on most maps? No. Hell, some don't even use 2 properly. Is it enough to secure 5k+ $ funding on Patreon? Yes. Then why bother? It can be useful, but it's more for self-gratification.
