I'm going to assume you're building a typical kit car street rod and not planning any major departures from the FFR kit. For cost & continuity it's better to get all your major assemblies at once. If you time your purchase you can take advantage of FFR sales -- I saved $2,600 by waiting for the winter sale last year. You will find that there is a lot of delay waiting on parts so the more you have on hand the less you have to stop progress on your car. Even a total kit will have lots of backordered items that will straggle in over months. The more parts you have on hand when you find you need something you can simply jump to another area and continue while waiting on parts to arrive. If this is a donor build you can start shopping for a parts car or individual parts now. There will be lots of disassembly, inspection / repair, and cleaning on a donor build. If this is a new parts only build you will still have a lot of assembly work on the drivetrain components so order them now. You may want to build an engine run-in stand to ensure your crate motor or donor runs with no issues and you can do some preliminary tuning. That would get a lot of this work out of the way before your kit arrives. Whatever you do plan to have fun -- this is a journey not a destination. Once your car is on the road it'll be fun but you'll still have thoughts of how you're going to build the next one and make it even better. Hot rodding is an addiction.