All the advice you got so far is spot on. I'll share my comments from my recent experience doing the same repairs to my car (though I have a N52 which is easier to access). Coolant flush and oil drain isn't necessary when replacing the oil filter housing gasket. I removed the oil filter and used a syringe to suck out as much oil from the housing as I could (less than a cup), and when removed there was only a drop or two that spilled. When removing the coolant line, either where it enters the housing or the other line bolted to the head to the left of the oil filter housing, about a pint of coolant may come out so have a pan handy to catch it. There's no need to flush, just make sure you top off with fresh coolant after you're done.
There are two bolts on the oil filter housing gasket that are a real pain to access. One is under the intake manifold at the rear of the housing, and the other is the front lower bolt which is right next to a connector where coolant
enters the head. For the rear, it's easiest to access with a 1/4" drive with E10 socket like this:
https://www.amazon.com/Stanley-Proto.../dp/B004USO7WK I only had a 3/8" drive E10 socket which was too thick to get between the intake runners and ended up using a standard hex socket, which unfortunately didn't allow me to torque it properly. As a result, I still have a minor leak at the rear of the OFHG because it's not torqued correctly. I now have the correct socket and a new gasket on order, hoping to redo it this weekend.
The lower front bolt is also a pain to access and is easiest done with the coolant line removed. Unfortunately the plastic coupler that is connected to the head is most likely degraded and will crumble apart when you remove it, so be prepared for this. If you don't want to remove the plastic coupler and risk breaking it, you could get a ratchet wrench like this:
https://www.amazon.com/Apex-Tool-Gro.../dp/B000HBF5LQ however I figured it was safest to replace the coupler and hose because that's one less thing to possibly fail in the future.
The serpentine belt and tensioner replacement aren't necessary unless they are either showing signs of wear or misalignment, or you don't know when they were last replaced. In my case my tensioner was bent and the belt appeared worn so I replaced them. When I was done I looked at the old belt and it had some cracking on the underside between the V grooves, so it looked well past its useful life. I was able to complete the job start to finish in under 30 minutes, so it's very easy. Just make sure you have the T60 driver bit to release the tensioner.
As for the eccentric shaft sensor, mine didn't showany signs of leaking oil so I didn't bother changing. It's worth replacing if you don't know that it's been replaced before and don't mind spending $, but I left mine go. If it fails, then that's another valve cover removal and replacement, and after having done it once already it shouldn't be too difficult to do a second time.
N54 has steel valve cover bolts as far as I know, so they shouldn't need to be replaced. They don't hold much torque and are very unlikely to be broken therefore they can be reused. (N52 uses aluminum bolts which cannot be reused, I had to use a new set)
Also, there's no need to use permatex.