Step one - I would take some business/accounting courses to help with the decision making processes.
Step two - Minimum economy of scale/barriers to entry.How much do you need to invest in the business initially to be competitive.This is really what kills 90% of motorsports businesses.Most of the time for a brick and mortar business to survive you will need at least one major "anchor" franchise such as Polaris or Kawasaki for example.After market suppliers usually give existing retailers some protection.See what wholesalers (Parts Unlimited,Fox etc.) are willing to talk to you in your area.
Step three - Have enough cash reserves to give the business a fighting chance for survival.You may need to pump money in for two years or more - that's right,no money out during this time.
Are you physically/mentally up to the task?Getting a business off the ground is enormously taxing to your health.
If you go the store front route remember "location,location,location!".
As TMKIWI said, advertizing usually yields mediocre results and by far your best return will be by word of mouth - generate as much goodwill through your shop as you possibly can.
Are you mentally up to the task of dealing with costumers? One friend (40+ year family run business) gave me this advice:"No matter how much you would like to leap over the counter and choke the living sh*t out of a customer - just smile". It's just a business and don't take anything personal.
Thieves will be watching your every move and will clean you out the first chance they get.The only way to keep them out is steel - lots of it.Bars on the windows,jail doors,posts in front of overhead doors,send them a message - they are not getting in.
As your business grows the banks will treat you like toxic waste - be VERY creative at raising capital.
Be prepared to work ungodly hours.Many times I worked from New Years to the end of February (when spring work started to come in) non stop - over 35 days in a row to keep the lights on.
And lastly,for now, enjoy yourself.The whole process is very challenging and satisfying and give yourself enough "breathing space" to enjoy this next step in your life.