How do shaved seats work? Is it a DIY jobbie or do you get someone to do it for you? It obliviously impacts comfort right (less padding/foam)?
A professional basically cuts/shaves the foam out to make it flatter or thinner.
Yes it removes comfort but for many it's a case of rising said bike or not.
Another option is dropping the forks and changing the rear spring but that's always a massive compromise on handling.
Can one go to training without owning a bike? How does it work? You borrow the training schools bike? How long does training generally take and what does it cost?
Yes most beginner schools give bikes.
Anything from a backyard mechanic style setup for R500 for 5 hours to the BMW 2-day course which is a grand a day I think. Ask Sinbad he did it recently.
Wouldn't a 750cc or 500cc be a bit much for a first timer? I was thinking of maybe a 250cc or will that be too 'pap' for the highways?
Cc is not a CC is not a cc.
Vast difference between a 85-100kw 600cc-class inline four Japanese superbike or Triple and a Parallel Twin 650-750cc with half the power and more torque.
A 250cc is way too little in modern 4-stroke terms for the highway. It will do 120km/h at absolute full tilt.
These modern 390cc class bikes are a better option but I still reckon a 650-750cc Parallel Twin second hand will be a better deal than a 390cc new.
If money is the concern then a second hand 390 class is probably not a bad deal.
I would definitely go for second hand, not new. I am less than 80kg

(need to put on some weight

)
Are most motor bikes manual or do you get automatic ones too? Is manual preferred or does it come down to personal preference like with cars?
Scooters are mostly automatic. The only proper automatic bike right now available locally is the Honda NC700/750 DCT. It's technically a manual with an electronic clutch but works the same. Yamaha have an automatic FJR1300 but not sure if you get it here and not what you are looking for anyway.
So manual is really the norm.
There are also the quickshifters on bigger more expensive bikes. Still have a clutch to pull away but can shift up and down without it after that. It's my preferred middle ground option for "automatic".
One other thing, I have a Cochlear Implant, which doesn't seem to fit well when I'm wearing a helmet and loses connection with my implant so when wearing a helmet I would be 100% deaf, would this be a major safety issue?
Not really. Over 80km/h you can't hear jack **** anyway due to wind noise and should be wearing ear plugs anyway.