Scuba lessons aren't cheap, and the minimum gear you need to take lessons is more expensive than you expected. So far, you have invested a significant amount of time and money into your diving. I have found that if you don't own your equipment, you won't dive as much for various reasons. Primarily as you have read about, safety, but also convenience. Tomorrow I will be boarding a buddies boat and going diving, but the local dive shop that we use is closed due to Easter. Besides, I am good friends with the manager and he said that he is out of rental tanks. Not an uncommon problem during busy diving seasons. I don't have to worry about these issues because I have my own equipment. If you go the rental route, you probably won't dive much, or any in a couple of years, and the time and money you have invested so far will be for nothing.
In regards to what gear you need to buy, most expensive isn't always the right answer. Decide what features you want ie:weight integrated BC or weight belt, do you want a diver adjustable knob on your reg or not, air integrated computer or not. These are questions you want to ask yourself. Most importantly, does the BC fit? How does the regulator breath? How complicated is the computer to use?
Finnally, DO NOT BUY LIFE SUPPORT EQUIPMENT ONLINE OR THROUGH A CATALOG!!! Life support equipment is what we take underwater on each and every dive. You have no idea if the BC is going to fit when the mail order gets to your door. You have no idea how well the regulator is going to breath if at all. How old is the computer and how long have the batteries been in it? Better question, how long before the battery fails and will you be under water, or above? Purchase locally and support your local dive shop and these questions will be answered.
Rmember, buy at your local dive shop, even if you spend more money, the payoffs if your LDS is actively diving will outweigh any savings you would get online by far. Also, you don't need to buy the most expensive, get the best fit, and the features you are looking for. Don't let someone pressure you into buying the next higher level piece of equipment to make them more money, if the investment isn't going to make your diving experience that much more fun.