Great project idea. I hope someone takes it! For now there seems to https://lemmyverse.net/ available for the interested ones. (tho it's not like instance "selector" you've mentioned)
DoT uses the TLS protocol as far as I know while DoH uses the general HTTPS (443) protocol. But both of them are encrypted so you shouldn't worry about security with any of them. Just use the one that is supported with your device/app
SyncVSFOSS thing isn't over yet? Let everyone use what they like the most. Let everyone be the judge of their own data and how it is being used. For god's sake, live and let live folks
There was iframe support while posting and then it was scrubbed off due to security reasons. I hope it can be brought back again securely or some other method exists.
That's why it's good idea to avoid the major/big instances and host on your own if possible (or choose some small random instances and check out their Blocklist+rules)
You seem little lost