It's interesting start so far DMG... I'm not familiar with the base but some random thoughts I'll throw out there...
The size of the ship is incredibly small while Star Wars sort of shows the ships (space anyway) to be of some bulk and size. Even a Snub Fighter like a TIE or Y-Wing is still a large and bulky ship when compared to a person... So that has me leaning, at first look, to your ship being a bit small... Speeder-ish in size more than a space-faring vessel if that makes sense.
Speeders in the film are clearly small, and that's maybe an advantage to them being used in combat.
Now, the next thing I'm noticing is a critique on the parts choices... Namely the two incredibly large cannons on the rear of the craft. The cannons are almost the length of the vehicle and given the overall lack of bulk to the craft, it starts to conflict sort of... When you look at the armament on a vehicle in Star Wars, usually a weapon has some bulk backing it up... For instance the cannons on the Snowspeeder have their bulk in the rear portion of the Speeder with bulky sections in the middle as well. The craft is small but there's a definite LOOK of where the "power" for those cannons comes from, if that makes sense... On your vehicle though, the cannons seem to just come out of the sides in the rear with nothing to substantiate the large guns being there... It doesn't look balanced then because of that.
In short I think I'd consider dropping the cannons first... They're just "too much" on such a small vehicle...
The overall shape is awesome though, very alien, and so is the bubble canopy... I dig that overall look. Some painting, some weathering/damage... It can make a really nice airspeeder, I just don't see it being a "combat" speeder or a space ship/fighter due to the small size.
If you've just GOTTA have guns on the vehicle, I'd go with a limited/small forward mounted cannon, perhaps just on the one side even... Something akin to the way the cannons are mounted on the twin-pod cloudcar. The guns are small and actually recessed into the curve of the forward hull on the speeder. They are a much more believable armament for a tiny craft like that.
Now, here's a thought too... And kind of ironic.
If you simply turned those guns AROUND, maybe made the portion where they connect to the vehicle a bit more "bulky" and solidly mounted to the hull (more like they're built into the body of the ship than sticking off the body), you'd have actually interesting looking engines that extend out past the back of the vehicle...
It's a little hard for me to put into words, but just looking at your first photo that seems like it would make the vehicle a bit longer, and look like it had a bit more of an engine to it too.