[DNSB]

Item 1, I am not that familiar with the iPad Mini gen 4. My iPad Pro has quite a bit more glare than any of my ereaders. In bright daylight, it makes a pretty decent mirror.

item 2, the ease of reading on an eInk screen? For myself, I can read much longer on my Kobo Aura One or Tolino epos (both 7.8" screens) compared to my iPad Pro. I do use the iPad Pro for reading pdf files which are mostly manuals where I am constantly zooming in and out -- reading a page intended for a letter or A4 size page on a 7.8" screen is not the greatest experience.

Item 3, the Kobo Aura One has what Kobo calls Comfortlight Pro. This lets you alter the colour temperature of the frontlight though taking it to extremes might cause the frontlight to be uneven likely, I suspect, due to fewer LEDs being used. On mine, the highest night setting makes me think of reading by candlelight but I seldom move the slider more than 25% towards the night setting and that is in a totally darkened room.

Item 4, the LEDs that illuminate the Oasis screen are single colour so no chance of a colour varying application.

One item to remember is both Amazon and Kobo use a Linux variant on their eInk ereaders. No chance of running an Android or similar application.

Item 5, yes, I use Overdrive on my KA1 and it works very well. The books are borrowed from the Kobo store and not the library server so once in a while I get a book that I am not able to borrow without going to my computer/web browser/ADE and then using calibre's content server to get it to my ereader wirelessly. I can't speak to the ease of using Overdrive with an Oasis since that is not supported outside the USA however some comments have suggested it is not quite as simple but still easy to do. This question would be easier to answer if you are able to add your location to your profile (no need to be exact but country/city/state/province helps with these questions).

Item 6, I'm not sure about the prevalence of glitches between Kobo and Amazon. Both have their share though Amazon has the advantage in controlling the format of their ebooks whereas Kobo has to deal with the variety of epubs that can claim to be standard compliant. Overall, I've been quite happy with my Kobo ereaders. One thing I like is that unlike the Kindlles, you don't need to jailbreak your ereader to be able to customize the reading experience or add additional reading software such as KoReader.

I would say that given what you wrote about screen size, clarity and blue light filtering, the Kobo Aura One meets those needs. With the assistance of calibre, you can purchase your ebooks from virtually any source and convert them to your needed format though that may need some assistance from Apprentice Alf.