Hey there,
First things first: the Seagull file seems to be corrupt. Dunno if something's wrong on my side, but please, check it out on your side too.
So I've finally got round to attempting to model a couple of ships. My first attempt so I'm learning as I go.
Please don't get me wrong when I say
it shows. The Kingfisher's mesh is kinda...sloppy, for lack of a better word.
BUT.
The idea is good.

The concept is good.

The overall shape is good, if a bit...simple.

Try adding some engine pods, extruding some side structures, something to break the 'two cylinders joined together' look. It's not a
bad look, as I said above: it reminds me of a pocket submarine. But it requires
some variation.
Good to see that you're LODing your mesh

: many modelers, including me, don't bother to, until the mesh is textured and done, in which point we're out of motivation.
As for your workflow: if Thaeris saw your mesh, he'd
scream about you not using quads instead of triangles. I'm not one to talk, of course. See, it is my belief that mesh errors can be avoided if you keep the whole mesh...a single mesh, without 'broken off' pieces (such as the cylinders in the end of the Kingfisher's wings). That means that using triangles to patch up holes and join mesh pieces is unavoidable. But I
do find it easier to start working with quads and keep working with them as long as I can. Dunno how soon you triangulated the mesh, but what I got was a lot of triangles.

(although, upon seeing the mesh again, I notice that they're arrayed in quad formations. So, I guess the triangulation was pretty late.)
All in all, a good first attempt, with lots of room for improvement. Don't be discouraged. My first model consisted of three boxes and a twelve-sided cylinder, all greebled to the max with an automated greeble plugin.

I think if made some giant leaps since then, and all I can say is, your second batch of models will be good and your third
very good. Just don't give up.