1/ leathers are fine and will be on the provisal they have a cotton lining not a synthetic one. You'll probably struggle to fine Cotten lined ones as they are generally in made to measure race suits. You can take the linings out and put a under suit under that is cotton and you'll be fine.
2/ bike wise you need to make sure it's straight, no frame cracks, jon Hughes at JHR race engineering in Swadlincote makes chassis and always has used frames and forks etc. the best thing about him is if you bend it he'll straighten it as will Maidstone moto liner Ray or Tommy. Stua are a good cheap package used by lots of racers but they are changed a lot in a season by riders.
Make sure when you but a chassis the wheels are straight when spun as well as the clutch none should move up and down or have any bearing play. Carb wise when you warm the bike up it shouldn't over run and check inside the carb to make sure the slide isn't worn into the casing.
Engine wise cheap and chearfull to maintain is a Jawa but ideally you want a std out of the box one. Ideally stay away with anything that says tuned,head by so and so etc. the basic the better.
3/ steel shoe colomonoy can be purchased from joe Hughes international through there web site but Alan bell ham is good for next day delivery. You can put it on yourself with a map gas torch.
Gearing for where your riding down south I'd be surprised if you'd need anything below a 60 rear sprocket and stick to std ratios 63/56 as its old money but everyone can relate to them.
Upright conversions are fine but like most things it's all about who and how it's been done. For the price you can get a dedicated lay down as cheap as chips. Long stroke or short would ok.
I saw a old upright on here eBay recently that was just a frame but I recognised the bike as mark walshs which had been stored. That would be ok as I recall all his bikes were at the time immaculate.
In a nutshell you just need something that starts every time and does lap after lap.
If you get stuck I have a current bike for sale with a good genuine engine that would be serviced before it was taken.
Good luck and I hope thus helps.