As for the crossbow, I don't think I'd give it Cumbersome. The point of a crossbow over a bow is that anyone can use it. You don't need some sort of extra strength to use the weapon. Unless, you fluff it that you need a decent Brawn to reload it. In that case I'd give it some sort of special rule of Slow Loading unless your Brawn is 3.
A crossbow is, by and large, a more cumbersome weapon to shoot than an actual bow. I'm speaking out of mild expertise, as an avid hobbyist archer, even if my experience with crossbows is limited to more anachronistic models. While its design makes it easier to shoot, the overall need for it to have a large length and width makes it unwieldy.
That, and bowcasters are Cumbersome 3, too... so I'd take my queue from FFG in adding Cumbersome to the crossbow.
I stand corrected and difer to your wisdom on this subject. I suppose fluff for cumbersome on the bow is because it's hard to pull the string back while on crossbows it'll be because it's just a big clunky thing. Depending on space-age materials, and intent of the weapon design, dropping it to Cumbersome 2 might not be a terrible idea. My understanding is that in previous games bowcasters were hard to draw back, which is why only strong Wookies used them, and might be why they gave it Cumbersome 3.