STOGEY:
I did learn something though, its good to make sure that you are familiar with your equipment before I make a dive.
Familiarity is one of the reasons for owning your own gear. If you don't own it, then certainly a good look over is important. Not all BC's have their exhaust valves in the same place and being able to reach one quickly could be critical.
When buying gear, everyone has their own order of importance. Most places you need to purchase Mask, fins, snorkel for your course, most around here require a weight belt too. After that, my recommendations (and reasons) are:
Exposure suit, usually a wet suit to start. Hardest to get a good fit, condition from rental and rentals get beat up quick, so often half the cost of a rented package is the suit, so fastest return on your dollar.
Next, Regs. Your life depends on them providing air and they do not take abuse well (dragging through sand, not rinsing properly, banging them around). If you own your own, you know their history and how they've been treated. Do try and dive several makes/models before buying though. Most regs out there are OK, but you may find some you don't like. I had one that directed the incoming air at the back of my throat and cuased a gag reflex. Dove em twice, they breath GREAT, but not for me. My son OTOH loves them, especially as they have a very compact 2nd stage. Other things are where the exhaust valve is, path of the exhaust bubbles might be in yor field of view and annoy. You may not like the purge, too small and hard to find (cold water issue especially with heavy gloves) or too large and inclined to flow facing inot a current.
Then BCD. And as you noted, there are differences. AHrd packs, soft packs, one cam band or two. Weight integrated or not, jacket or back inflate, or maybe BP/wing (they're not just for tech diving anymore).
Along the way you'll pick up tools and gadgets you won't want to be without. You'll certainly want at least one good dive knife. Lights (night diving is a whole new adventure), safety sausage, whistle or horn, your own dive flag/float, maybe a reel.
You might want a dive computer (and you might buy it with your regs if you want an air integrated). Here again a wide variety. Different sizes, console mount, wrist mount, hoseless, more/less conservative, larger/smaller numbers (how good's your eyesight), backlight. Some you can change the battery yourself (with an easily available battery), others you have to send to the manufacturer. Before you spend $$, talk to other divers, see what they're using, why, what they like about it, what they dis-like.
Generally the last thing to buy is tanks. Tank rentals are usually pretty cheap. You have to go to the LDS for fills anyway and some shops it's leave them and pick them up in a day or two, so you're not even avoiding an extra trip to the LDS. If you take a dive trip, you can't fly with your tanks, so you'll have rentals there. Add in the cost of annual Visual inspections, hydro every five years, you have to dive a lot, to save money buying tanks. On the other hand, owning your own, they're filled and waiting in the garage, you can do those last minute dives when the LDS is closed.