I did my tank on my old mk3 golf. DOn't tihnk there the same, however I don't think the process would differ.
You can do it yourself, however I would have 2 people as it makes it a bit easier. On the mk3, the filler neck was all one piece on the tank, so removed the straps and angled the filler neck with the tank out and it dropped.
I got my tank from my mate how does vw spares in Bonnybridge. He sold me a good tank from a vr6 for £40 as VW wanted hundreds of $$. If it is close to you, I can check to see if he has a mk4 lying around.