I have 4k miles on my J costa and wondering what my pins look like.

It's about a 20-30 minute job start to finish, check as often as you feel you need. I have noticed that with the aftermarket belt that there is not as much (belt) dust as with the stock. There was a report of an aftermarket belt that disintegrated (shred itself) but only the one report. I'm not sure how to answer your question.

Like Paul said, it is a 20-30 min job. I just changed out my sliders, putting back the 28 gram sliders, and then entire job only took about 30 mins to do. So checking the belt should only be about 20-30 mins. I have a Pictorial in the "Pictorial" section so look at that first a few times and then do it. If you have a cordless drill with a phillips head screwdriver, 8mm socket, 10 mm socket and some allen wrenches it will go much quicker.

Per the owner's manual and the service manual the Clutch Shoe Wear Inspection interval is every 4,000mi (6,400km). I don't hold too fast to this interval, but am generally close. I'm not as fastidious (anal/OCD) as some.