I don't know this engine all that well yet, but when the engine experts wake up and read this, they will want to know the miliage on the engine first of all.
When were the valves adjusted last ?
The rough shifting into 1st sounds like too much slack (freeplay) in the clutch cable adjustment.
There is only a few RPM difference tween 4th & 5th kinda like an overdrive. When up shifting, if you hold upward pressure on the gear shifter untill the clutch is fully engaged, can make for more positive shifting. It is at times the "nature of the beast"
PS..........
Welcome to the forum,.....you are for sure in the right place.
Be aware,....there are several here that when it comes to these bikes, think they know it all, and they do !