It's OK Ed, My knowledge is only a cupfull based on what we both don't know, LOL. A few things to consider, one, most models at the warehouse are unfit for use in FS. They are way to heavy on polys, have too many textures and are modeled with overkill on detail and quality in mind and not any use outside of the warehouse. they are great for learning to model though and many can be stripped down, but I find that it usually takes longer to do this that to create one from scratch.
MCX has a Create LOD (level of detail) button. What this does is decimate the model based on a couple of methods, it's usually less than satisfactory, but it is good for creating an empty LOD which means at a certain distance the model does not display. You can also create multiple versions of your object, each with less detail/parts deleted and import each one at a different LOD with the simplest being at the lowest LOD. On your haybales, I can just barely see the LOD I created kick in as I am flying away, but if you are not looking for it, you won't notice it and that LOD took the model from 19000 polys to 759 polys at that distance.
Triangles or polys are bascially what the mesh is made of, the less the better, but really the thing FSX focuses on more is drawcalls which is the amount of textures and the converter in MCX isn't that reliable. i always make a single texture sheet BEFORE I do any modeling and them assign the textures that way.
It's funny, if you think Gmax is confusing, go d/l Blender, it is free and way more robust than Gmax, but the interface will throw you for a loop! LOL. I use it from time and time again when I need to get .LWO or lightwave files into gmax and it is great for texture baking.
Just some FYI to help you out, you are doing great!!