i just installed my aFe stage 2 intake on my N54 last night. by myself, it took me about an hour, but i also wasn't rushing.
not sure how much different the N52 model is, but for me, the hardest part was getting the damn rubber grommets from the OEM air-box to seat properly in the aFe housing. took a good bit of finagling and a lot of curse words.
other than that, everything was pretty straight-forward, so i'd rate it around a 3. again i'm not sure if the N52 one is much different.
'88 Porsche 944 - SOLD
'90 Audi Coupe Quattro - SOLD
'07 E90 335i 6MT - SOLD
'08 E90 335i 6MT - SOLD
'13 BRZ SportTech 6MT - current