I don’t own one but would think the biggest problem would be starting up costs as you know good bikes and stock can be expensive.
Other concern I would have is getting the big names like Specialized allowing you to be an authorised dealer. Without this you really can’t sell their stuff as you need to get their ok to ensure that any Warranty is valid.
also not a great time to start a business as you know but in other ways it is. Banks are following over each other for new small businesses after the governments buy out scheme has now forced them to lend. Speak to a local business enterprise as you might be able to get a start up grant.
Sorry this might be stuff you already know and have thought of but was just something that came to mind when I read this.