Hey there!
The "blank" xmls, support the "blank" ship sets. These ship sets set all the standard designs as "AI ONLY" so that you never see a default design when playing, and yet, the AI will still utilize them. I tend to make all of my designs whilst playing, from scratch, because the defaults are pretty sub-optimal.
So its merely for convenience for those who don't want the defaults in their way and are tired of obsoleting stuff.
And thank you, I'm really happy you are enjoying it! in terms of designs, you'll be happy to see the next sets... they are the "novelty" styles of ships... kinda gimmicky, but cool to have... we will have some robo-bug ships, truly organic space-squids, and living crystal ships soon!
The Zerhan are cool, I was a little lazy and one day will revisit them to add more unique hulls for their Huges and such, but I'm very happy with their colors and designs. My Terrans are not GOOD GUYS in my universe, so the "brutal" comment makes me happy 
I can't pick a favorite either lol!
@franco fx
That design or similar styles is certainly possible. Its not really my forte though, my ships tend to be "solid" I just naturally avoid ... frailness...? Anywho here would be my advice:
1) First, figure out what the engines are going to be. All ships in a set, should generally have the same overall engine style... it helps tie them together and makes mass-design production faster.
2) Design your turrets/weapon systems as custom components. Its best to do this first, so that your subsequent designs know what things to anticipate mounting, and their shape. I didn't do this with most of my sets and I learned the hard way... which led to some ships have some not-very impressive weapons. I did this perfectly for the Kirani and it really stands out.
3) I would stick to Altarian and thalan parts, but use the various Iconian tentacles and sink them into the hull to create "filigree". Will not be easy, but should work well.
4) I would use the same colors/textures that I used for the Jun-Jilar, would get you that nice metallic purple that this image has.
5) Remember, that you should NEVER base a ship part off of a custom part. Always put down a normal simple central part. Never attach anything to a custom part if you will be scaling the custom part.
6) For that simple, 1st part, not a bad idea to make that part a central piece that will be a theme of the hulls in general.
