For the selection of the system, I would suggest to discuss the different system licences which are available to us, based on three or four main criteria:

First, how well does the system fit to the setting, so the compability of fluff and crunch. This should include the usual basic rules at first. It's neither impossible nor unthinkable to adjust the system with homebrews etc. but that is another step, and since every systemcan be modified, it is not a very solid arguement anyway.

Predictably, the adaptability of the system is another arguement, meaning how good or bad the system can be adjusted to the setting, how much work it does to do so and how much fun it is to homebrew stuff for it. Right now, I assume that we cannot use any system right out of the box, without any adaptations, adjustments and lots of extra stuff, therefore the  

As a third important question, the market penetration or probable success of the system and the number of potential people who could be interested in this. It might be unfortunate, but  even the best system in the world won't help us if noone has ever heard of it, or plays it. The opionion of those who are actually professionally active in the distribution of RPGs is especially important in this regard.

And finally, the personal taste and experience of the matter should not be neglected. Everybody knows that it is easier to work on something you like and appriciate, and thus the personnal preferences should be involved as well.