Welcome jdb1989, pretty old school for me to know much about your 500. I can tell you, reeds are very important to performance and its easy to imagine running it hard and then breaking corners off of them. The fly wheel does look rusty, but if you are getting spark, you might wait on that for now. Clean air filter, fresh gas, clear silencer and exhaust, new plug ( B8ES NGK ), stuff like that. They can be finicky reviving them. Stuff settling in the tank, or carb, may clog up the jets or fuel line. Also have seen mud daubber nests and mice nest in the silencer cause funky problems with a resto.
First I would find a manual for that year of 500, they cover 99% of problems and repairs. Mostly, you have to diagnose which thing to buy first, but rest assured that 300 bucks is just getting your foot in the door
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I never have had to pull my bike. If it won't kick start with a new plug, I know its not going to run well. Maybe, that could get necessary with high compression head or something, but its no good when you have to resort to that. Usually that will cause more expensive things to happen. Hopefully, you will find it as a simple problem, but start with the basics getting a solid baseline to start from.
