"Which color do you consider more appropriate for a pair of dressy Edward Green slip-ons: Burgundy Antique or Dark Oak? I’m specifically speaking about the Kibworth model, which I will wear with a blue blazer & dark grey trousers."
You wouldn't be making a mistake with either color. Dark oak can be worn in more situations in my opinion, but burgundy, like the pictured shoes by Hawaii's Leather Soul, is very nice as well.
"I have been habitually using double pleats, with cuffs, for my suit trousers (high-waisted, of course, with braces), and getting my odd trousers cuffless with flat fronts (and a Daks waist, as I can't stand belts). Although I am slight of build and have no trouble wearing flat-front trousers, I'm beginning to think that I might prefer pleated and cuffed trousers for wear with odd jackets as well.
Do you pleat your trousers in casual fabrics, such as moleskin, corduroy or linen?"
Jeans and other work clothes have typically had flat fronts, so moleskins and cords can go either way (linen is a dress trouser cloth). Forward pleats and cuffs are dress trouser enhancements that appeared early this century and have been with us ever since, though flat fronts returned in military uniforms during the Second world War because they required less cloth.
Flat fronts look fine on men with washboard stomachs but pleats are the product of more sophisticated tailoring. They are more comfortable and look better as the discipline necessary to maintain that washboard disappears later in life. Pleats do not need to be accompanied by cuffs, though cuffs are customary for double breasted lounge suits.
Like the pictured twill trousers from J. L. Powell, all of my trousers have had cuffs and two forward pleats since I was a teen, irrespective of the state of my waistline. But then, I don't own any jeans.