i'm also 21, so i don't have tons of experience, but one of the best things for restomodding is to plan everything, and re-plan everything. Have everything planned down to the valve stem caps you want before you start. Price out everything, and decide at the beginning if you should make changes to your design so it better fits your budget. It not a good if you don't plan and have a budget for 15k and after spending 13k still need an interior, wheels, tires, bodywork, ect.

My original budget was around 12k, after 4k i'm almost half way to having the car how i want it, but it's gonna be over my budget in the end

i've been working on this project for 2 years, and will prolly be another 1 before it's on the road, and still another before it is completed