I think you should try for the same use year. It makes managing the points much simpler. On the other hand if you come up with one of those deals that you really can't turn away from, don't be intimidated by separate use years. I have two and it isn't an issue. Are you an organized person? You have to be much more organized when you own more than one use year. Many others on here report having more than one use year and not having a problem.
If you did find a contract with a September or October use year that suited you, it would work well for your October and New Year's trips. You could then use the April use year for the May and August ones. Having 2 use years would help you in this case if you had to cancel your October or New Year's trips, you could still bank the points.
HBC