Welcome to the forum,
Looks like you have a good project there, lots of work to do, but looks like you picked it up of a good price, to get it onto the road it will have to pass an IVA controlled by VOSA, have a search their latest manual is available for download of the site.
Chassis number you can make your own up, or apply to DVLA for one, if you go your own way then 17 digits is the format, again have a search their is a post on how Dave Smart used to format them, although your chassis pre-dates Dave.
Insurance, call Graham Sykes & Adrian Flux, I've insured off a chassis number in the past, but only whilst I took them to Vosa/DVLA to get them on the road. But there maybe other schemes for part built kits, lets face it some people have many many thousands wrapped up in their kits.
You sure they are Golf callipers all around? they look like Mini up front, but it may have had a disc conversion on the back to Golf. If you do go down the road legal route, then the mirrors will have to be moved outwards, they will not show the correct rearward view as they currently are.
Members in Norfolk, Tiggersmini is in Norwich & Wally1 is in Suffolk.
Alan...