Thanks for all the input guys. I can't make this too long because I need to focus on the now and go study for my calculus exam tomorrow, although I will touch on a few points.
Firstly, I'm definitely going to take everyone's advice into account, and I've taken up both Joel and Scott on their offers for info. I want to be as informed as possible, and most likely, I'm going to work in something totally non-scuba related such as business or corporate as an economist after I graduate. I'll probably work as an economist for a few years while I completely wipe out (I'm talking everything, car loan, student loans, everything) my existing debt by getting a well-paying econ job (they typically start out at 50-60K for a bachelor, 65-75K for a master's, and I'm getting a master's in applied economics since it's only one year extra and will have many courses directly applicable to running a business) so that when I do take out business loans, I will not have a crushing amount of debt to my name.
I'm extremely computer savvy and I grew up with my dad running a business so I am well versed in marketing, management, etc. that is required to be successful. I plan to not only run the dive shop but have a separate web site devoted to internet sales of dive gear...it makes no sense to just have a product catalog on the web site for a dive shop when you can instead have a link to a internet sales site. The customers who go to that dive shop will still have the security of ordering from someone they know since the sales site is ran by the dive shop, and it can also be operated as a separate business strictly dealing in internet sales. A dive shop that stocks a full line of scuba equipment is already set up to run an internet venture like that so the only real additional cost from it will be the cost to maintain the web site, which I know from personal experience, will be a very small fee. I can actually maintain the web site myself since I happen to know HTML, so the only cost for the internet sales site will be the $50/month to for the server hosting and the shopping cart.
Ok, as far as the dive shop itself goes. I won't have commission-based sales because, and I'll stress to the customer, I want what's best in the interest of them and not have people selling gear to them simply to make their own paycheck fatter. I'll do this through offering a reasonable base salary to the employees. Repeat customers will be something I'll adamantly try to get for obvious reasons. Very few companies survive without a lot of repeat business. To start, I probably will only have maybe one or two employees anyway so it won't be a big issue on payroll. I plan to be trained as a maintenance tech in all the scuba gear I handle, as well as be an instructor in all the classes I teach, so I need the minimal amount of employees possible for starting out. I'm aware that the goal of a business owner is to make a good return on his/her investment while he/she is far away from said business, however, I'm ok with putting in 8-12 hours a day to get it going since it will obviously be far cheaper for me to do stuff myself than pay a bunch of people to do it. And before I get my customer base built up, obviously saving money will be key.
I plan to market intelligently, as far as that goes. E-bay is an excellent source of virtually free marketing; many businesses sell products at discounted rates on there which not only makes people want to buy from them repeatedly but they have links to their store in the product description of the auction so they get "hits" on their web site from the auction as well. Obviously, even the discounted rate yields a profit or there'd be no point to doing it so the firm is still making some profit /and/ getting high-yield marketing out of it. I'll be doing other stuff too but that's one example.
Lastly, I plan to do a lot of research on the numbers and open a dive shop in the place that makes the most sense. IE not a ridiculous amount of competition which will encourage price wars, good (and growing) customer base, sufficient demand, etc.
Ironically, even though it's not a business degree, using calculus techniques from an economics perspective I can even find out the price to set for each product that yields the maximum amount of profit.
Anyway, speaking of calculus, I'm off to study so I destroy this exam tomorrow. Thanks for all the input guys!
P.S. if anyone's wondering, since I'll have 3 years inbetween graduation and starting the shop anyway, I do plan to get a good amount of dives and skill proficiency under my belt before doing DM and beyond.