I am no expert on rigging - thats Disturbing 13's area of expertise.
I can say though that Milkshapes JT exporter is excellent and outputs correctly for use in FPSC - if there are errors then they are in the file itself - not Milkshapes JT exporter.
As to the texturing Milkshape should import a deault FPSC character model with skin correctly applied and export it with the same credibility. Together with Fragmotion these two programs should be enough to achieve whats needed - what one dont do the other will.
With user created models it may be a different matter as how well they work and how well a skin texture is applied depends upon how and in which program the original model is created and the mapping info is generataed
Creating, rigging, animating and skinning character models completely from scrtch can be fraught with difficulty and problems. I dont think I could do one in a day - more like a month for me and then it would probably look like a road kill.
I have great respect for those that do so. Take my hat off to you I do.
I have enough problems taking a default FPSC character and amending it - not sure which is the easiest or hardest method - all seems very much like hard work to me until you spend the time to master all the disciplines.
"I am and forever will be your friend"