Hi. To have a winning website in this field you will need to do several things:
1. A solid marketing plan that reaches car enthusiasts (there are many ways to do this - Inbound marketing, influencer marketing, adwords, seo, etc... we can discuss more if your interested)
2. A nice looking website that is user friendly and allows users to find what they are looking for easily and quickly. Finding car parts can be tricky.
3. Good dropshippers, preferably based in the same country as you for larger or more specialized items. (You can use Ali Express for smaller and more generic items that will ship quickly)
4. The proper plugins to make your shopify site work like a proper sales funnel. eg. retargeting, remarking, email marketing, abondoned cart recovery, etc... All this stuff should be automated so you can scale the store and your not focusing all your time on administration of the store.
5. The right partner that knows Shopify inside out. Not just building stores, but how to market the store as well)
Let me know if your interested in discussing more. We are a Canadian based digital agency that focuses are building successful Shopify stores.
Take care
-Sondeep