• what do you want to learn?
• risk management
• cost (budget), time (to build), scope / complexity: the iron triangle

General principles which can guide any project, can also be applied to tomfoolery like "making a car." Like if you're bored or something.

What do you want to learn?

Cars are complex and this might be a long, frustrating project. Figure out what parts you want to figure out, and what parts you'd rather just have ready-made. Some project options might be (say) "build an engine and put it in a mostly-working car," some might be "take a mostly-working car and build new frame around the guts," etc. Knowing where you want to directly contribute can help narrow the search for your next project.

For me: I wanted to learn the end-to-end assembly, but not new construction techniques. No welding, but start from 'scratch.'

Risk Management

There are a lot of potential risks with undertaking a biggish project:

• you're sending maybe a lot of cash to someone who might be hard to go strangle (figuratively)
• the thing-you're-making is probably rare, therefore hard to just... "test drive"
• what if you screw it up? Nobody wants to spend time and money failing
• what if the backing for your project... dries up? these things take time, companies come and go.

References go a long way here. Being able to find a working version can help get past the 'test drive' problem, and can provide some sense of stability for the supporting community. Having a community of people who have done this before can help ensure your support for the inevitable "why doesn't tab A fit into slot B" kinda issues.

Ditto, history can often -- but not always -- help assuage concerns of a company becoming insolvent along the way. Unfortunately this is probably a huge risk. Lotus keeps getting bought & sold, for instance. Westfield up and vanished. OTOH Factory Five have been around for a while and may stay. Exomotive supplies relatively little direct parts (or support) and may not really be required post-shipment.

For me: the 7 community is pretty well-supported, if you look hard enough. Density is relatively low, like 1 example per region, but they're out there.

Iron triangle: cost, time, scope.

In project management there's the concept of a triad of conflicting axes: cost, time, and scope are often selected. These tend to directly interact with each other: constrain time, and you may have to flex cost or scope. Specifically, you can do things faster in exchange for money (higher cost) or less things-to-do (reduced scope). Or, "more scope will increase time or money (or both)."

In "project car" space:

• cost is m-o-n-e-y. Less money almost certainly means more complexity or longer time... and you can buy lower complexity and faster delivery.
• time is calendar time, in two forms: time-to-acquire-stuff and time-to-build-stuff. Some projects can show up quickly (project car -> new car), some can take months or worse (kit from UK + JP + CN -> boxes in driveway). Assembly time can also play a role: some projects might be months or years of assembly, some maybe weeks. In exchange for potentially higher cost or complexity.
• scope is complexity. "Rebuilding a 30-year-old engine" might be fairly complex. "Designing an electric powertrain" might be very very complex. "Assembling a kit from reasonably well-understood parts" might be ... less complex. In exchange for longer delivery time and higher cost, of course.

I ended up with ~12-16 mos of shipping (partly because COVID / supply chain) and ~2 mos of construction. We're not talking about the cash, but a benefit of "this is a 2-year project" is that much more time saving up...