I definitely would like to figure it out eventually. I've been modding with just XML for like a decade and figuring out how to make buttons and icons last year was a game changer.
Model design has absolutly nothing to do with XML modding. The only common point is... CivIV. It comes down to comparing playing tennis and playing guitar.
Assuming your future creations are intended for CivIV, you should start with nifskope (which will allow you to bring models in the game and modify various anim parts) to understand the NIF basics (I use 2.0dev7 for models and basic anim modifications). Only using blender involves you will have to find someone to effectively convert your creations for CivIV.
For modeling, on geometry stage, start with easy things. Avoid curvy objects, with lots of backsides and impossibles counter-angles. Take time to learn the XYZ concept, to make tries and failures with the various commands, and not loose yourself with complicated automations, which are only efficient if you have a strong knowledge of 3D in general and python coding. Try something like reproducing A7V, then Jagdpanzer VIII, etc... Then later, you'll be able to do more complicated things.
To give you an idea, the Hellcat is too difficult for a rookie: too much curves (not to help, they added a kind of bubble effect on straight lines to give a cartoon-ish visual effect, which was in the mood 25 years ago), assymetric forms (there's not even a square or a regular triangle in the structure), unlinked parts...
Once you're done with your shape, pick up a "telling" texture: I mean a picture/assembly of pictures on which you will EASILY find where to put your UV. Don't hesitate to use orthographic view projections instead of automated unwraps, which are risky. I personally use three to five views pictures still, and will probably never bother with making a puzzle like the standards require.
To give you an idea once more, for a rookie, your Hellcat is impossible to texture with the files you actually have.
All these steps are time consuming. Actually, your model should take me between five and eight hours to build, texture and animate. Two years ago, my first model took me three weeks...