Hi,
We finished our timberframe house last year.
We used Cellulose insulation in all external and internal walls and between the floors. We had open web joists between the floors. We had though about rockwool, but saved ourselves a lot of labour and time by getting a contractor to fit airtight membranes on all exterrnal studwork and plastic accross all interal studs and joists, and pump full of cellulose. It took a week to insulate every crevace in the house!
There is very little noise between rooms. Very happy with this
Between floors is good too, we put plywood on the upstairs floor, on top of this we will put underlay and then a timber floor/carpet. We haven't decorated the upstairs yet, but I don't think there will be a problem. My husband does a lot of work (with power tools) upstairs, and I can't hear them downstairs. Footprints can be heard on the ply, but this should be sorted out by the underlay.
We do have one problem with sound. The HRV pipework acts as an intercom! So for example the bathroom and utility are on the same extract line. A conversation in one room can be heard crystal clear in the other! Even though these are not adjacent rooms. Same issue with the hot air distribution from the fireplace.