Yeah, ok the Bachmann system is cheap, but I don't think its the best route. I picked up a cheap roco set on ebay (not much more than the bachmann one; about £40-50, including a sturdy transformer capable of a lot more than the Bachmann one! I then expanded and did some research and discovered that the Roco LokMaus2 works with Lenz, and I now have it as one of my slave units to my new system. The roco system also allows CV prograamming and upto 4 functions (including dirrectional lighting).
You can easily mix components between the system, like decoders, provided they are NMRA compliant. I have 3 or 4 different brands of decoder. The Bachmann ones are very good value for money too!
On converting to DCC its simple, just wire all rails together from a main 'trunk' power supply that runs round underneath with taps off it, only thing make sure your rails are squeeky clean for optimum running, but even if they are not perfectly clean then the locos (unless Lima!) will still run better on DCC than DC (I would advise against chipping Lima locos as they really have such poor motors that the advantages of DCC are fairly pointless, infact I was talking with the owner of my local model railway shop and we agreed that its much easier to go for DCC fitted or at least ready if you are a beginner, as the locos are designed for DCC and so have perfectly cleaned and maintained pickups.)
So to sum up you need;
-Lots of wire!
-A base unit control system and transformer
-DCC chips / locos fitted with DCC chips
-A bit of patience and perserverance (I've never looked back)
Just some of my ideas hope they help!