I have to agree with SeN, unless you have the mechanical aptitude to do this don't attempt it. Apologies for the bluntness of my next comment BUT if you have to ask if you should replace you valve cover gasket after inspection you probably don't have the experience to do this DIY. If you f#ck this up the result will be very expensive. You can buy the kits you need from Pelican and have it all fedex'd within 36hrs.
In a former life (yes I am that old) I built race car engines and have done valve adjustments and VANOS rebuilds on all the E46's I've had and it's certainly not the easiest DIY you could tackle.
If you do attempt it please make sure you take your time and have plenty of patience with it and if you get stuck dont guess, give a shout out and there should be someone around on the forum who can help you out.