Dj, there are 4 hydro shops in the area, htgsupply is in southborough, and there is another store near haverhill and a few others in the south shore.
I like your idea of starting another one... but here's your basic idea about starting a biz.... first I suggest you spend some time on sba.gov -- then you will need to research suppliers and wholesalers, then you will need to get a resellers license and permit, then you will need to located space to lease, then you will need to register a business in the town you decide to do business in and with the state -- it is a very lengthy process, and takes full time dedication -- sba.gov can show you how to apply for business loans to get you up and running -- and there are websites out there that can help with that too, like prosper.com and google sites for 'social investing' -- I have a few links that I can supply you with if interested...
And there's a possibility if your idea is good I may think about talking with you -- Im looking to start a business, and I have a little cash to invest with -- might be something worth looking into...
You do know though, hydrostore owners don't make much money -- the overhead is fairly low, but so are the profits in a competitive market.