Your local and state safety laws should be pretty clear from their applicable Web sites, but make sure you're very clear on the requirements if you're looking into street legality for your vehicle. For many, this step doesn't really come up until they're close to completing the rebuild -- but you should have a good idea of what the final requirements are going to be before you even start. More than one hobbyist has seen his dreams -- whether for using the car daily or simply riding in a classic car parade -- dashed by the seemingly last-minute needs of the state.
Areas to keep in mind for this part of your project budget include everything from fuel source and emissions to safety regulations like mirrors, brakes and indicator lights. The law of the road is intended for day-to-day drivers, not classics, and in pursuit of street legality you could find yourself making changes you're not happy with.
Almost any regulation is something you can eventually meet, but if you ruin the look of the car or it takes away from what attracted you to the project in the first place, you might end up feeling ripped off. Be very clear about what you want from this car, and make sure you understand the rules and laws by which you'll be allowed to have it.