[Steve]

If you are gonna buy a euro, then the engine, gearbox and chassis goes together in a day and ties up lots of cash, which you might not need at the start of the build. You the have to store it while you work around the body.

If you fit the body to the chassis too early , then there are parts of the body (around the engine bay) which you need to access to make a good job of the finishing that are obstructed by the chassis

The body is where most of the time is spent, (and in the early stages, jobs like gel coat polishing, flash line removal etc are time consuming yet relatively cheap), so id look to get those jobs done first, and wait till you are ready for the chassis.

Given the GD (and other manufacturers) delivery schedules.......

I'd get the chassis and body on order now, (you can decide on euro vs jag nearer its build slot)

decide on engine and gearbox If you are gonna buy an off the shelf engine, delay its delivery till you are close to having the chassis, if you are gonna build the engine yourself, get that sooner

dont bother getting wheels and tyres till you have the car almost ready, (you can work more easily with smaller Donor wheels fitted and less chance of getting them damaged)