will have to test that one. What are the supported sites? One more thing is how user friendly it is.
Tachiyomi is not officially uploaded on fdroid. So i don't recommend using it. Download the version from github even tho they are the same.
Now for j2k, it doesn't take a lot of time. I don't think so. Just backup and restore in j2k and select the same download folder. That should do it.
Poweramp and WACUP
Why go through emulator when u have better alts. You can try mangayomi which is still new but has a lot of options and very light.