Descents, while complex, are usually fine if you plan ahead and keep on top of it by continually analysing where you are. There are a few things to keep thinking about such as distance to go, the wind, the altitude you need to lose, the weather, turbulence (eg if you need to come back to the turbulence penetration speed, then the VS may need to be reduced), cabin pressure, ATC requirements, minimum safe altitudes and approach steps, other traffic. The point is that everything has an impact on a successful descent. It is not just set and forget. And as to the approach there, I would probably chose a normal RNAV to try as the 340A isn't equiped in the real world to do an RNP approach. With RNAVs generally, you look at descending 320ft/nm. So work out what height you want to be at each waypoint and then depending on the speed set a vs that will make you achieve it. Hope all that makes sense.
