Get the drysuit!!! You will dive much, much more once you have it. You will also enjoy some of your dives much more, because you'll be warmer, less tired, etc. The advantages to the tank aren't that great, after all, you already have to go to the dive shop once, going a second time shouldn't be that hard. As for the course, since you have someone you can borrow from, go ahead and do that. Maybe borrow the equipment a little early and try it out before the course begins. And, as was pointed out earlier, after you buy the drysuit, you may later be able to get permission to buy the bp as a necessary piece of gear because you took the class.
BTW, have you tried getting your wife to dive? Maybe you could enroll her in an open water class as a "gift" because you want to share diving with her. If she dives, buying gear will get much easier, as long as your willing to buy for her, too!
otter-cat