Kevin gave you some great information. The OEM footpeg on eBay is a good price for what's included. I'll try to shed some light on the popping.
A well tuned 900 with a pipe AND jet kit should idle smoothly with no popping. I've never heard a 900 pop at idle like that. I'm gonna say that there is one or more cylinders that is running very lean. Almost like a really bad misfire. I also noticed the revs tended to "hang up" a bit when you blipped the throttle. A properly running 9 should sound like this:
Now, to help you out with your problem, I would recommend removing the carbs, take an inventory of the main and slow jet sizes, vacuum needle position, and fuel mixture screw turns out from lightly seated. Once that is done take the carbs COMPLETELY apart and clean them. Make an initial fuel screw adjustment to 2.5 turns out from lightly seated. Once properly cleaned and put back in the bike have them synced. I would recommend doing this yourself, and buying a manual. I've been working on 900's for the better part of 23 years. They are one of the best running bikes when properly set up. It's not rocket science, but carbs can be daunting the first time you tear into them. I have tons of carb photos I can post for reference if you need them. But if it were my bike the carbs would have already been out and on the bench in the time it took me to type this. Whether you do it or a shop does it, it needs to be done. Good luck, welcome to the forum, welcome back to motorcycles, and congrats on the new to you 900RRW.
One more thing, I don't know if you know, but the first picture has the bike sitting really low. Did you know the triple clamp is like 2" lower than stock? Looks like the rear as well. FYI only really.