I see you’ve found other threads to answer a few of your questions, but for the other questions…
I THINK it’s generally up to the software to handle decryption keys and such. You should still be able to use a first gen BD drive with current BD releases. (Note: this doesn’t include movies on 3 & 4 layer recordable BDXL media, or the newer Ultra HD BD media, which super old drives can’t physically read). So just keep the software up to date and you’ll be fine.
Yes, burners are generally more trusted than Combo drives or ROM drives. I can’t fully articulate why, but that’s my current understanding.
I can’t speak on USB enclosure incompatability issues (though people may have specific recommendations, as I’m sure you’ve seen).
And there aren’t many models I would tell you to stay away from, though note there is a Samsung slim drive that has quality issues (the slim external SE-506CB) when writing BDR/RE media. And LiteOn models don’t tend to like LTH media, though we generally recommend HTL media anyway.