The video looks good and I'm gonna make a rip for myself anyway so might as well post it.
MeguIVit was created for people who know absolutely nothing about encoding(you don't even need to install anything, just download an exe and extract a folder in the same place and you're done minus a potential small bug with some settings that require another step) so they could rip JAV and idol movies very easily and with high quality. You could leave everything to its default setting and you'd make something that looks good with almost no chance of problems since everything is detected automatically.
The hardest part is knowing that in 99% of the cases, you need to drop the VTS_01_1.VOB file at step 1 since that's only explained in the first post of the thread and not in the post with the pictures I linked.
You can even make 30fps rip with it if that's what you prefer(60fps should be a problem at dvd resolution though, but for bluray it would indeed be much more demanding).
The mkv vs mp4 thing in my signature is only for my encodes since I usually make 3 version for JAV movies, it's not about mkv vs mp4 in general.
There's zero difference between mkv and mp4 for the video or audio quality since they're only containers. I could put the exact same video and audio in either a mp4 or a mkv.
The main differences between the two is that mp4 has more commercial support(it will usually play directly on video game consoles or dvd/bluray players and things like that which is rarely the case for mkvs) and mkv has more features(you can add titles to them, it has a very advanced chapter system that can even allow to use multiple files as one video or have one video with different versions inside if you want to censor some scenes or have alternate endings) and better tools to mess with them(joining, splitting, appending other files in multiple formats, etc) as opposed to mp4 which are much more limited.
Depending on the video player you're using, it's quite possible that mp4 works better because of the commercial support.
Them being more space friendly is just a coincidence or that people have a preference of compressing video more when using mp4, but it has nothing to do with mp4 vs mkv.
Same thing with the details, the video and sound inside has nothing to do with the container, they'll look just as good inside an mkv than they do inside an mp4.
You can see plenty of stats with mkv(probably more so than with mp4) so I'm guessing the reason for you noticing that is that the application you're using to look at them doesn't support reading them from mkv as much as it does with mp4.
Subbers usually prefer them because they're easier to work with and modify afterwards(mp4 are a pain to work with if it's not like you wanted and have to redo its configuration). The groups that use mp4 is usually for compatibility with more devices and they'll usually hardcode the subs on the video instead of using softsubs which can be disabled.
If you don't need the extra features of mkv, then you're better off using mp4 because of the wider compatibility, but if you want the extra features, then mkv is the only way to go. The picture and sound will look and sound the same either way.
I use mkv for my better rips because I add a title(which I can't do with mp4s) and I've had to use the edition feature a couple of times to make a lesbian only version and a full length one of a movie without having to make 2 separate files and it's not bigger than simply making only the full length one(except maybe for a few KB, but that's negligible).
I used mp4 for the poor quality smaller file only because I wanted them to be easily identifiable. I could have used mkv for both and it would be the same, one with great quality and the other with the poor one and small size.
As a side note, you can make a 1080p rip(or any other size for that matter) with a DVD by simply resizing the picture when encoding, but you'll be wasting a lot of space and it likely won't look better than if you kept the original resolution so it's rarely a good idea to do so.