I sometimes use the 270 (10) Most of the time I use the 210 (15) I have a Juki 1541 that the 210 will work on but not the 270. I also have a 1508NH that the 270 works beautifully on. I have found the 270 does not work on the medium weight upholstery machines like the 1541. They werent designed to handle that size thread. Machines designated "heavy" can handle the heavy thread. I use a #22 needle for the 210 and a #24 for the 270. Hope this helps. You will love the thread.
It looks like it is all tension related. Sergers are very touchy when it comes to tension. Be sure that your top thread (yarn) is running freely. The top picture looks like your yarn tightened up causing the red(lower) thread to pull up.
If you deal with SMS long enough you will be the recipient of a poor service experience. They have their moments of getting it right but they under deliver way too often. They say they are working on improving customer service.
When applying glue to anything, a minimum of cleaning the surface should be done. If it is a painted surface a quick sand or scotch brite will improve adhesion. A little prep time is better than redoing it later.
There are stickers posted on our building that state there are trace elements in the building that are known to cause cancer in the state of California.
Dry silicone spray works great for helping slide covers on. Andy is correct in that you don't want to be spraying it anywhere near where you will be doing any painting.
I prefer 3/8 but its up to you. Go and measure a bunch of car seats, see what you like best and what you think looks better. The gauge on the machine can be changed if you buy one and decide you don't like the width.
Richpeace and Tajima also have CNC perf machines. They also have a combination machine that perfs and quilts for those hard to do complex stitch patterns.
Eliminating as much bulk as possible is always a good idea. Some machines handle it better than others. A new feed dog will help pull the fabric through.
Its is possible what you are sewing is just too thick for the machine to feed evenly. You can check to see if your feed dogs are worn out and not pulling the material through as they should. They are not that expensive and only 2 screws holding them in.
Matt, is that 30-40 cents a sq in for everything? Panels, seats, flooring? Do you calculate your area by the amount of material used or do you actually measure each seat and panel?