I started working at a Raleigh pro shop when I was in high school. A fun job for sure. The one thing I hated was when they tried paying us wrenches commissions instead of hourly one summer. The rest was fun.
When I graduated from college, i was managing the failing shop by then, they offered to sell me the bike shop. Yeah, I could see it was way in debt so no thanks. I left after 4 days of new ownership. 4 days too long. The new owners torched the place within the year.
Now some 35 years later, money making career job over, I am now managing the local bike coop for no pay, just for fun and rewards of doing good.
A few things I've learned over the years.
Paying rent is the surest way to fail. (applies for housing too).
Borrowing operating funds is the next way to fail.
Paying for advertising never pays.
The shop I worked at in high school & college did all 3 and overpaid the owner and his family hobbies. Plus the huge inventory was called the local warehouse by other lbs. There is far more variety in parts now. Trying to stock everything is impossible. One of my never ending pet peeves is when a store workers tells me "we can order that". Well so can I this age of the internet and it will be cheaper, faster, and delivered to my house so I don't have to make another trip to your store. I've seen a lbs pay $250 for overnight shipping for a pair of wheels to keep a customer happy. Yikes.
I've seen several successful shops started with a group of investors / workers. 4 seems to be a good number. When the shop grows and succeeds, the less interested owners can be bought out by the others. In fact, putting buyout methods and prices in the initial agreement can give everyone specific goals to work for.
Running your own business means you work when you aren't sleeping. Like 12 hour days, every day. You need to learn to do your own accounting and taxes and payroll and bill paying and do all that on time.
Bikes are a never ending irregular cycle of fads that fade but never die out completely. Pretty much every kind of bike ever made is still being made, some in very small numbers. You can become an expert on any one but none will be a raging success. High wheelers, mountain bikes, bmx, cruisers, road racing bikes, touring bikes, unicycles, commuters, gravel bikes, tandems, recumbents, etc. You simply can't deal with all of them or even more than a few. Need to focus on what sells, not collecting dust and interest payments. Many styles are age dependent. Guys still want what they wanted when they were kids but now they can afford them. Once that generation is gone, no one wants that stuff anymore so the prices plummet.
One old school bit of advice was to start small, as a repair business. Well selling new bikes is far more profitable. It's the core of all bike shops. Hiring decent help plagues most businesses. Selling parts and accessories is limited.
Another way bike shops carry on is to inherit them. That's usually done from father to son. Good luck with that.
which provides for decent pricing on stuff for the most part. But there are a few of us scouring and battling Craigslist to get to them first. 
