1-
I've managed in the last days to make few tests
If we are talking about the same 'Priority' parameters :
then, by testing, I saw Upload and Download were shaped by this parameter
I had 3 devices, each one connected to one of those subnets
I set up the Uplink configuration to 7Mbps to simplify calculation,
keeping in mind that Priority High = 4/7 of Uplink config, Normal = 2/7 and Low =1/7
I downloaded big files with the 2 devices that were in Normal and Low Priority subnets, to saturate the link
At the same time, I was making speedtests with the device that was in High Priority subnet.
I got 4 Mbps download with the High Priority device, which fits calculations
I cranked up Uplink config to 14 Mbps, just to be sure
I got 8 Mbps download, which also fits calculations
And it also worked with Upload tests
2-
And for point #2, yes Bandwidth limit will override Priority bandwitdh