SamyGO

Hope that's the one you need, that's all I had in my "TizenSDK" folder (don't ask more )
https://mega.nz/file/ulZEBRhZ#xYIb6LvzP ... a4fya8WtoQ

You can't

Link works currently, don't think it ever stopped to

The frame is quite exotic model and looks to remain "L series" every year so far. You may find correct letter (where I moved your post) after second number though, like all other Q's. Otherwise you can simply trust launch year

TV just won't accept firmware with different name. No upgrade, no brick

A usual PC is powerful enough to default to sw when no hw support. TV not.
Your TV series is where you posted

Nope, no root for you (yet, or at all).
"Codec" is usually a hardware capability on powerless SoCs, so there's never a chance to "add" one anyway.

Both same, just typo (T-NT14MJ doesn't exist actually...)

Nope.