Beginning to modify - advice?

[eeep]

Hi all.

I'm looking at buying some bits and pieces to start modifying my MK2 at some point, and these were the sorts of things I was looking at, any advice, feedback or suggestions? Price is a major factor at the minute, so I'm looking at picking things up to fit them at a later date.

Induction kit
or replacement filter?
Boost gauge and controller

I understand that new spark plugs and some adjustments to timing would also be needed? I'm pretty much a noob at cars, and this is what I've gathered from reading various threads, including this guide.

Cheers, Mike.