Everything I'm about to say, I mean with utmost respect...honestly, I do.
Based on the questions your asking, I do not recommend a DIY here. The E90 VCG change is a totally different animal than prior year models. I am a fairly good DIY'r with a descent tool collection, and failed at this one.
I had several complications. First, the reason your VCG is leaking is almost certainly because you have broken head cover bolts (super common with this engine). Depending on where they are broken off, this can get tricky. Second, when you remove the cover, I would give 10:1 odds that you break the oil separator hose that connects to the cover. Without proper tools, this can be challenging to replace. Third, once you get the cover off, putting it back on requires an angular torque wrench to properly secure it. You will need a digital wrench here, as you will not have enough room to get in to the aft bolts with a angular dial.
This job on this particular model is not for the faint at heart. It is labor intensive and time consuming..and requires a bit more than basic tools and skills. I'm gathering from the questions you asked (ie removing the spark plugs) your aren't equipped for this.
My friendly, humble advice (from someone who tried and failed here) is to find a local BMW Indy shop and just pay then to do it. My local shop quoted $400 including parts....WELL worth it.