I use way oil for everything but the gears, where I use a 00 cornhead grease, as it is cheap. It does fling out at high gears.
Consensus on oil is that anything is better than nothing. SAE 30 is almost certainly fine, if not exactly what was intended.
I wouldn't buy leather unless you are rich. This stuff works very well and is 1/10th the cost:
https://www.mcmaster.com/5753K431/ Search "flat belting" for more options.
Clipper #2 is good for up to 3/16", meaning you will get the least amount of click. I got mine off ebay. You'll want at least 12", your belt will stretch over time. Take the belt off at the end of use period.
Those are what I used on my Royersford Excelsior 21". You can see how those turned out, link in my sig, if you want.
I hope that helps.