I am wanting to start a small shop to sell Atv's, Dirt bikes, Motorcyles, etc, Where do I start? Do I need to ask the dealers to become a dealer first. Or can I just do it.

Normally if you want to be a authorised dealer, you buy a dealership ( franchise) from the company. Normally they will have specified fees, min order requirements and so on.

For example some years ago to be a Briggs and straton dealer we had to do a opening order of 10,000 in parts and supplies.

So decide what brand you wish to be a dealer for and contact that company for their requirements.

Also, is this something that you are going to want to do full-time or in addition to a job that you already have? Will you be wanting to operate out of a storefront of some kind outside of your home?

As Chuck pointed out, delearships like these have to be authorised by the manufacturer. Generally you start as a Honda or Yamaha or Kaeasaki dealer. Once you can show volumen and stability, you can add other brands.