In terms of cheap parts to replace, the fuel line is very low quality. Orchard or home depot have better fuel line. You already replaced all the bolts and studs, that is good, otherwise that would have been the first thing to do, cheap bolts caused me more problems with my first kit than anything else. The spark plug and spark plug boot usually fall apart pretty fast (my spark plug failed on the first test ride). A good replacement spark plug is the NGK B6HS. Any decent carbon core spark plug boot from the auto parts store will do. Chop one end of the boot off and unscrew the old one from the CDI, then screw on the new one in it's place. The fuel filter is made of cheap plastic and will crack easily and spill fuel everywhere. Use an in-line fuel filter meant for a lawnmower or the like. Throw away the fuel petcock, it is useless and doesn't actually do anything. Go to the hardware store with your gas tank and buy a barbed brass nipple to replace it with. You may have to re-tap the hole, as they usually have metric threads. Depending on what kit you ordered and what upgrades you plan to do, you might also consider replacing the chain. The chain quality varies wildly from kit to kit, I had a chain that broke pretty quickly. #420 chain is good. On some bikes it is possible to get rid of the chain tensioner entirely. If this is the case with your bike, you should do it. You may be able to use half links if the chain isn't the right length. On hub adapters, it sounds like your hub won't work, but I can't say for sure unless we get a picture and accurate measurement of the diameter. If you choose to try the rag joint, the wheel should last long enough for you to decide whether you like riding, but it probably won't last more than a hundred miles or so. If you replace the wheel, you can get a rear wheel with double walled rims, 36 triple laced spokes, and a disc hub for about a hundred bucks at performance bicycle. Then for another hundred or so you can get a nice disc adapter and a custom sprocket for 420 chain from rebelgears. I would recommend upgrading the sprocket because the stock one is cheap and I could literally bend mine with my hands, so I don't trust them. If you have a drill press (or if you're really patient and careful, you could probably get away with a handheld drill), you could also make your own disc adapter for a lot less, I can walk you through it if you want to go that route. In terms of more complex (expensive) upgrades, the first one is that your engine will probably 4 stroke from running too rich even at the leanest setting on the carb. To fix this you will need a smaller carb jet. The air filter is also rather ****ty and restrictive, a cone air filter would be a lot better. Also, if you want more power and speed, make yourself a good expansion chamber. A good one can easily double the torque of these engines, as the stock exhaust pipe is a piece of garbage which has the engine way choked down. If you want to see what I mean, try removing the end of the muffler and pulling out all the junk inside, then ride it around the block. It will be loud as ****, but you'll see a noticeable difference in power. Don't ride it this way though, you'll annoy people. A good expansion chamber will provide even more power than just removing the end of the pipe, and it will not be nearly as loud. You can also port the engine with a dremel without too much trouble. Hope this wall of text helps give you some good ideas.
, are always by my side. Not to mention it's 20 degrees and falling, outside, and I'm bored :-\