The evil is in the number of mods.
If you're going UI, you'll need:
"Fresh" install of IL2:1946
Patch 4.08
UI 1.1
Patch UI 1.1.1
AFAIK you will need to apply the latest "AC Installer" each time you install an aircraft. Latest at the time of this post is 3.6 and it can be found in a Hurricane thread, with the Hurricane for carriers.
Now, which mods? I have not installed any myself yet, as I was only occupied with making the P-38 cockpit. From what I've read, these mods should probably be on your list:
JAFA's sounds (Link on Youtube, not AAA. There his alias is JAFAEM)
Flushies bumpification mod
HolyGrail&Potenz 3D smoke and what-not.
Propeller Mod V1/V2?
There's a "Gore" mod, but that's if you want the realism upped to include bloodied pilots in their cockpit.
You'll also want to get improved cockpits for the aircraft you tend to fly. There are quite a few out there, like BF109s, Spits, P-47s and mine and Poncho's project ,
the P-38.
You'll want to look at maps too, I guess. You can focus on MTO (i.e. Malta), PTO (i.e. Kokoda, the Slot) and ETO (i.e. Channel map, NW-Europe). Some are W.I.P. and some are not 1:1 scale.
Another thing to 'fear' is the WW1 project called "Canvas Knights".
Edd will probably add his recommendations to this list.