No you are not a car dealer because you are not buying or selling anything. You are an agent/broker acting for leasing companies and paid a comission. A 'middleman' and part of the financial services sector. You correctly identify who the dealer is in your post above ('5' and 'b') in your two lists.
You are not selling cars and you are not marketing cars, you are marketing financial deals. Your customer has most likely already decided which car to buy, the spec. and the colour (probably as a result of visiting a dealer and having a test drive). They then trawl the internet looking for the best leasing price. When they pay money for the car they pay the financer, you take a commission.
You are not a dealer in the same way that my insurance broker is not an insurance company and a mortgage broker is not a bank or a builder.
I am not knocking or criticising what you do. Good luck to you. But what you do is far removed from what used car dealers are doing. The kind of marketing that you do is not relevant to most of us.
The key skills in being a successful used car dealer is (a) knowing how to buy used cars you can make a profit on, and (b) interpersonal skills - handling your customers.