Saying that most of the "fat" is removed is not correct. It IS fat. You convert from a Fatty acid to FAT of sorts. The things to filter out are the waxes, glycerol, and water emulsions that are formed during the refining process. Yes, 1um filters are great, IIRC the last I saw 2um was the industry standard. Most people that need to filter are the ones using KOH to dry their stock.
The ONLY way to keep it form gelling is to either cut it with somthing like RUG or Diesel, or to somehow make the carbon chains longer or polyunsaturated. Unsaturating fat chains causes the melting point to plummet so it gels at a much lower temp. It is easier than extending the chains usually. There are people out there currently using specific enzymes to do both. I bet getting these enzymes would not be too hard, but then you get out of the normal individual area and into the "hey I got a back ground in biochemistry" area.
For a deacent referrence on a great bio D set up look for the Dirty Jobs episode where he went to Tacoma, WA to work in a taco shop. They went to a guys house and showed how it is done.
I get you question now about the diameter of the molecules. You would not typically catch molecules in a 1um filter, only complexes of molecules.
Also used are sock filters, and gravity filtering. To each their own.
Any filtered WVO can be run. Hell, non micron filtered can be run, too. Diesels are amazing in that they run on just about anything compared to their gas siblings.
I am glad that I am not the only one interested in such things here.