You can use Porter's "five forces model". It is designed to help determine the average profitability and sustainability of a business within a market. It is one of many tools.
1. The threat of new entrants
High. Low if you go the bar + homebrew route. Many people probably bail on the idea when thinking of dealing with tabc
2. Rivalry of existing firms
High. You are in competition with awesome webstores and established brick mortar shops.
3. The threat of substitutes
High. The internet is a powerful business tool and larger online shops may be able to out price you
4. The bargaining power of customers
High. Again, the internet and the other shop in town
5. The bargaining power of suppliers
High. You will probably not be buying in bulk and may not be able to price your wares competitively.
(not looking good )
I think homebrew shop + bottle shop\bar is a good idea. It gives you a way to increase your revenue and another reason to get people to come to your shops. See Dr Jekylls in Arlington
I wouldn't use this model to compare a LHBS to the internet. Its like comparing a farmer's market to a national grocery chain.
I could definitely save a lot of money by ordering brewing supplies from the internet, but my brewing experience would not be nearly as fulfilling and a LOT more frustrating. You offer many services the internet cannot:
1. One-on-One troubleshooting - even faster than forums and more specialized.
2. Technical expertise - when you buy a new piece of equipment from a LHBS, they can show you how to use it... no sheet of instructions sent.
3. Instant gratification - I buy my supplies on brewday. If I forget something (gypsum, irish moss, pH strips, rice hulls, etc.) I can run and get it. Internet = nada on this one
4. Social interaction - our LHBS has homebrew kits to sample on tap, and its a great place to hang out. They also have classes (kit/all-grain brewing, winemaking, etc.), host the Big Brew, and help put on our annual state homebrew competition.
I apologize for slamming on internet brew shops - I think they are a great resource and would utilize one if I didn't have a LHBS in my area. I just really wanted to convey that the internet shouldn't scare you away from starting such a great business!
Good luck to you!