I agree with T-ster that the ZDZ-60 will be an excellent engine for this plane....but at those weights it is right on the edge of needing to go to the 80, but the 80 would also be on the side of overkill. T-ster is right that if it comes out on the bottom of that weight range with the 60, it will probably be all that you need. It all depends on what type of flying you are planning on doing.

T-ster is again right that a "real" thrust number would be helpful, but as far as the numbers ZDZ posts, forget them, they are virtually worthless, at least if you are using them as absolutes. They are based on calculations using a thrust calculator. You would find that actual thrust readings will be 20-25% lower. If you want to compare power to other motors, check the RPM readings from the various engines using the same brand, type and size of prop. As far as actual thrust numbers, there is very little data available on this, though it sure would be helpful.

As far as your original question "Is it the only factor?", no the other important factors are reliability, cost, smoothness, ease of starting and weight. The ZDZ60 and 80 both do well in all of these categories....except I've heard some posts about difficult starting from a couple of sources.