Are the MPP (v1.6.5d Beta) and the http://www.nexusmods.com/morrowind/mods/40947/? supposed to be used with one another? Is UMPP even necessary with Quorn's update? Also, should I be using the Unofficial Bloodmoon patch?

UMPP is the old version of MPP, so installing MPP is enough. I am not sure about Unofficial Bloodmoon patch but I use the official one at the very beginning of my install.

UMPP (not UMP) was designed to be used with BTB's version of the patch, but with Quorn's update I'm not sure if it's still necessary.

http://www.gamesas.com/topic/1474127-mpp-problems-mistakes-and-suggestions/?p=23026512 requires assets from the previous versions. So I first installed MPP 1.6.5 BTB edit with assets from BTB site and then installed the 1.6.5d unchecking BTB version.

Sorry misread that.....

I already have done that. I'm just wondering if the UMPP fixes and the Unofficial Bloodmoon Patch are necessary.

Quorn lists the changes made and from the what I see from nexus page UMPP also lists the changes. So, to be sure you have to go through them to be sure.

But, the best man to answer this is Quorn, I guess.