Noob With a Few Questions

I have been learning as much as possible about e-commerce and have found the niche/suppliers needed. I would like some recommendations:

The niche has many products and brands associated with it. So, if I built one website I literally could have thousands of products on it and a hundred different brands. However, I would like to start making money soon and was going to focus on starting websites targeting specific products. I also am using BigCommerce so I can't afford trying to sell more than 100 products at the moment and building a giant website selling thousands of parts and many different brands would be too much at the moment.

For example: Niche = car parts (not real niche I am in)

I was going to build a website targeting two keywords within that niche. For example we will use: Ford Parts & Ford Air Filters

The Ford Air Filters is the keyword that I really wanted to target. It gets 4,000 exact monthly searches. And Ford Parts gets 1,500.

So the homepage would target Ford Parts and the category page would target Ford Air Filters

Then later on I was going to build a website targeting: Acura Parts

The thing is, in this niche with many products and brands, if I went with that approach I would end up with 100+ different very targeted websites to manage and possibly be competing against the same keywords.

So, should I just build one main website and start off just by selling the targeted keywords I wanted, and then eventually adding other brands and products to it overtime, eventually years from now having one giant car parts website?

So, I would just build one website targeting the main niche: Car parts
and to begin I would just start off selling Ford Parts and Ford Air Filters and then later on start adding to it by adding Acura parts.

Would I rank higher for Ford Parts and Ford Air Filters if I just built one website around those keywords or would it not matter and I should just start slowly building an entire website around Car Parts and then target the keywords on other pages on the website?

So, instead of making multiple sites like CarFiltersXYzzzZ.com and CarMufflersXYZZZZ.com

Should I just start slowly building one giant Car Parts website?