Starting a business isn't hard, but running it successfully and growing it is. I tend to agree that you aren't likely to make a fortune building guitars, but you also talk about owning a store or chain. If you do that part well, you can make money. But there are a lot of stores already selling guitars that are well run, so if you want to compete, you'll need to understand how they do what they do. You also need to know what the market is like, can you see any opportunities, what are you entry barriers. . . Lots of stuff.
You're 16, so you probably aren't going to open your business tomorrow. Go to some local music/guitar stores, talk to the owners about their market/customers, competition, the industry. Then go look at the big guys and see what they do. Maybe get a part time job at one of the stores and talk to the customers. If you figure out what the customers want and can deliver it better than the Guitar Center, you might have a shot.
I just ordered a small gig bag from Sweetwater. Nobody had it in stock, and Sweetwater's site didn't say OOS, so I ordered one. They called to tell me it was out of stock, wouldn't be in for at least a month, and offered to cancel the order. I said no big deal, I'll wait. Got two more updates and two emails to keep me informed, and then a follow up email to make sure the item arrived. I think they had the factory drop ship it to save time.
That would never have happened with Musician's Friend. When I ordered something from them in November for my daughter, I received an email saying the item was OOS and wouldn't be shipping until January. Bit late for a christmas present . . .
You can guess who I'll order from next time if their prices are equal. So here's a question for you, did Sweetwater simply utilize free employee time for all that effort, or did it cost them more because of the extra effort? I know that the guys in the Guitar Center are just sitting around 80% of the time . . . I don't know how well Sweetwater is doing as a business, but I'll try to use them in the future.
My point, slow as it is to arrive, is that you need to study the business environment. Learn the basics about customer service and business operations . . .
And make sure you read "Why we buy.", "Influence", and a good book on running a small business.
Good luck.
Todd