As for the decomp plug, read this:
Specifically your bolt may be too short to actually be blocking it correctly - see the image in that page section.
As for the cable, you can usually get away with just loosening the clamp screw on the starter lever, pulling it taught and retightening. If needed you can pull the cable out of the housing and remove both sections of cable housing and replace it with a single cable housing (with stock bars the housing is too short if you just remove the short section). Bicycle brake cables are the same and you can pick some up locally or on treatland.tv or doscycles.com. https://www.treatland.tv/6mm-housing-by-the-foot-p/6mm-housing-by-the-foot.htm if the end of the cable frays you can maybe cut the frayed part off and get it to wok, but if the cable's end is frayed you probably need a whole new starter cable. https://www.treatland.tv/SACHS-super-special-STARTER-DECOMP-cable-p/sachs-starter-decomp-cable.htm (just remove the short section if your decomp is plugged off)
And as for fluid leaking out the cable hole, that hole's not a tight seal, but if it's leaking out a lot it might just be you've got too much fluid in there.
also you might wanna put in an actual clutch cover gasket. treatland.tv and doscycles.com have them. https://www.treatland.tv/clutch-gasket-for-sachs-504-and-505-motors-p/sachs-clutch-gasket.htm without the space that the gasket provides, sometimes the starter clutch bell won't retract enough and it impacts idle and wears out internal clutch parts extra fast. plus itll stop leaks outta the cover and much cleaner than silicone goop.
Regarding tire, theyre not bike specific. I also don't know what kind of bike you have, looks like a Westlake? That only matters if you need wheels, but rarely do you need wheels. I think you just need tires. in that case, look at the side of the tires and it'll say 2.25x17 or something like that. that's the tire size you need. Pick whatever variety you want, you can get dirtbike looking tires that fit, or ultra high quality racing tires, or generic cheap ones etc. (if you wanna wing it' i'm 95% certain you need a 2.25x17) these are cheapest: https://www.treatland.tv/majority-of-mopeds-sava-mitas-B4-TIRE-PARTY-17in-p/b4-tire-party-17-2.25-again.htm and these are maybe the better deal (better rubber) https://www.treatland.tv/fashionable-racing-TIRE-PARTY-in-17-x-2-25-p/mc11-2.25-tire-party.htm
I'd order from treatland.tv, grab the gasket set also, and rder soon there's a code for 20% off that's in a thread in the general forum. get tubes, tires and might need to get some real tire levers too. ( https://www.treatland.tv/tire-iron-240mm-p/tire-iron-240mm.htm )
and order a spare tube because everyone pops their first one. even neo didn't make his first jump...