I would recommend sticking with the 1/4" eyelets, simply because it's more or less "standard", and using them means a client will likely NOT be contacting you, asking you to build another sheath when they try to use any of the available "fixtures"/"mounts".
As far a setting up for kydex, I too use a toaster oven, that I've wrapped in kawool. Here are images of my kydex press, built from a "hardwood floor jack" from Harbor Freight. The hard part is finding foam for a press.... the stuff that most outfits offer as "kydes press foam" is a joke..... anything even a tad over 350F, and you it will melt to your kydex......not only wrecking the kydex your working on, but also requiring you to purchase new foam. Personally I use silicon foam......it's pricey, but I've only had to buy it once.
Something I feel that is VERY important with kydex, is realizing that not every knife design lends itself to a kydex sheath! Kydex holds a knife via "pinch points", and that is usually the plunge cut areas or a part of the handle when a knife is designed to be use with kydex. If a knife has a large guard, be it oval or single finger guard, it's usually not a got candidate for kydex.....time/experience will teach which designs are good for kydex, and which are bad. Painter's masking tape is your best friend when molding kydex...... a layer or two on the item you're molding will give it the "wiggle" room needed when the kydex cools and shrinks.