Hi maciej and welcome to CS!
The questions youve asked are very basic. Have you really given this much thought or seen the roasters youve mentioned in action? Anyway, answers below:
1. How the heat (coming from the gas burner) is transferred to the drum - radiant heat and heated air
2. The shape of drum vanes - varies from one manufacturer to another
3. How the chaff is collected and carried out of the drum - also varies from one manufacturer to another, though generally carried out by air flow
4. How the drum is mounted to the chasis - axle
I have a 3kg Diedrich - your welcome to come and take a look at it...from the outside only!
I think youll find that there isnt much information available because these are registered, proprietory designs. Copying without permission wouldnt be appropriate. I think youll find that roasters respect that.
How about coming up with your own design?