Yes, “Automating multiple user accounts on single mobile” feature will be available by 17 Oct 2020 Update.

Theoretically kind of unlimited. The only limiting factor is that, how powerful is the PC (ram, cpu, etc.).
I've seen people automating 90 mobiles via ADB from a single PC with 32GB ram and some powerful CPU (I don't remember the CPU name exactly).

Yes, It is completely undetectable to apps. Like whether they are getting run by a real human or getting automated.
(Automation via ADB sends device input actions (touch/tap/swipe) directly to the android OS (as if they are sent by the real touchscreen)
and Android OS passes those inputs to the app.
Just like how your (real human) touch/tap/swipe on the real touchscreen sends the input actions to the Android OS and then Android OS passes those input actions to the App.
So, for the app, both are exactly the same, as, it is only talking to Android OS.)

It is as safe as if you hire some person to do the exact same Actions.
But do note that even real humans will get action blocks if they do too many actions. So, just use the settings accodingly.

Yes, we have plans to work on it soon in future.

There's no need for scraping. I only put things into place what and how a normal human would do.
Which is selecting/visiting target profiles via seeing them in comment sections, people who liked the post.

Yes. Just select “DIRECT ACCOUNTS” as the target type in target settings. And add your target usernames (one username per each line).

I mean I can program it to do that but that is not very humane. No real human just goes about swiping through 50k followers of a single account. And I think doing that will flag the account. It'll be best to get that targeted bulk scraping done from outside and add that list to NecoMancer IG as targets to Engage with.

Yes, that setting is also available now.