Rough in sense not smoooth shifting with a loud "clank" sound or it is noisy in any gear?

Yes, after some time, gearbox will become smoother, but picking adequate oil is also important. But I do not want to confuse you even more - you'll figure it out by yourself.

Also, you should check clutch cable - sometimes they are too loose and this clutch lever on the crankcase cover can not be pulled enough, so friction discs and plates are not disconnected completely, and as a results you'll hear that rough sound while shifting gears.

As regards this humming sound from the gearbox, there is no help. All gears are straight cut, so noise is their side-effect.

Oh my, this English drained me...