I've been dabbling with sketch up and ADE9x and I've modified Lydd airport (Kent, UK) with custom buildings, I've also modified aprons, runways etc.....

I don't want to upload the file for public consumption yet, getting shot down in flames, and yet I need some constructive feedback from folks.......I'm sure I will have to correct stuff before it's ready. What's the best way to achieve this?

Here's a preview:

I'm pretty sure you need to get a tester.  As far as I know, I'm pretty sure you need one before you upload something and get it on the site.  I know I need one, and as a matter of fact, I have 2.

If you made the textures, I have a few suggestions, but otherwise it looks great!

For the fire station and fire trucks, I'd say add some more saturation to the bricks and the trucks, and maybe make the trucks a bit more red or red-orange.  They look pink!   A rule for red:  If you're trying to make it pale red, make the hue a more red-orange than red.  Pale reds tend to look like a dull pink.
Add a bit more saturation to that blue/teal storage hanger.
Add some more saturation to some of the shipping containers and vary the colors a bit.
Then for the big white buildin with the Lydd (was it supposed to be Loyd?) Aero Club, darken the white/grey spots on the roof and make the spots smaller.  The roof just looks checker-board like otherwise.  Make the white spots on the windows and glass dark pale streaks instead of splotches, or tottally get rid of them.  They also look almost like checkerboard tile.


But even without those, it looks great so far!

I would think the big test would be its functionality in the sim environment... does the AI (if any) work properly? All of the PAPI lights work, ILS & NDB all work, etc.

Is the scenery for FSX, or for FS 9? I'd be willing to test it for you, if for no other reason than to see if the sim accepts it.