I have never embroidered on leather. Since I go to YouTube for most of my researches I thought I see what they have to say. Maybe this will give you some answers. Search for

Embroidery Hub Ep. 54: Leather Embroidery Tips

and good luck. Can not wait to see your project.

I embroider on a lot of leather for an automotive company who does custom upholstery.....sometimes I don't even use stabilizer. I slow my machine down a bit and use my normal isacord polyester thread and my every day needle. When I digitize for leather I use a sparser underlayment to limit the amount of needle penetrations...just test everything 1st on some scrap leather or vinyl ......hope this helps....oh, I use a 16 needle machine, that is why I slow it down a little.....

Use a leather needle and slow down the speed for a domestic machine as it will reduce the wear and tear on your machine and give a better result. If the design is dense it may cause buckling of the leather and the extra needle holes could make larger holes, so more open designs work well. i would float the leather and use sticky stabiliser, a magnetic hoop or if you are making a key fob you could baste the outer edges if you are planning on trimming excess away. Hooping the leather may cause rub marks or damage it. Always test on a sacrificial piece and make sure the leather is not too thick for your machine. I have some leather here that I would not ever attempt to sew or embroider with using a domestic machine as it is too thick. Industrial machines are a different beast and can handle most things. I would use tear away stabiliser but this also depends on the thickness of the leather and intended use. Can't wait to see what you make.

I have embroidered on leather, on nappa and on suede, the thicknes used for gloves and clothing - and used a universal needle or an embroidery one. A leather needle just makes too large holes for the embroidery thread.
I have sewn, not embroidered, leather rescued from an old settee, much thicker. It would have been a candidate for hand sewing, using the right tools: punching holes and using two needles to sew the seems. Which I did not have or intend to buy for a one-off. I did it by machine and used a leather needle. It makes small triangular holes and needs thicker thread than 40 wt embroidery thread. Made a nice and sturdy bag.

i use a clear silicone lubricant ( sewing slip agent) sprayed on the top it helps the fabric slip under foot, you can use it on any fabric, I use it on lycra as well....wendy

I have sewn on upholstery that looks and feels like leather, perhaps it would sew different, slow the speed, use a 14" needle and my regular thread and a more open design less stitch count.

One more added hint. Move your design start point so that the first time the needle goes down into the leather it is actually stitching the design. (Most of my designs have a jump start right at the beginning) Once you make a hole in the leather, well, you have a hole. :)