Hi Gazza
You can put as much or as little into building the kit as you want really and it's quite a personal thing. Do you want Carbs or bodies, what dials or digi dash etc but if you go for the Zetec kit, most of the bits you need are there apart from gearbox, diff and TIME. Any additional bits you need you will be able to make your mind up over the course of the build. It's not a weekend job and half the fun is building it from scratch but it will take you quite a few months (depending on how much time you allocate to it).
The Zero is not a challenging build and the car you get at the end is very good.
You will also find that the Club is a great source of knowledge and help. Fellow inmates (sorry, I mean members) will advise on this site or descend on your house for a home visit. The average Hoodie lives on tea and biccies and can sense a packet of hobknobs being opened from a distance of over 100 miles so bribery with biscuits is highly recommended.
I appreciate that the site is slightly confusing as to what you need to complete the build and have made that point but if you want a top class car that goes and handles to a high level, then the Zero way is just about the easiest and most cost effective way.
Go for it!!