As far as moving your apps pool to another set of drives, I have used this: HOWTO: Copy the hidden ix-apps dataset from one pool to another
You have to do this in addition to changing the pool in the gui.
I have had my apps disappear from the gui but still run in the background, but I think that unsetting the apps pool in the gui and then choosing it again made them appear. Seems to be a different issue here if that didn’t work.
As far as physically connecting the new drives, you could use the link above and copy all the app pool data to your large data pool. Then export the app pool within the gui. Then make a new pool with the new drives and copy the data back to the new app pool. Someone might have a better solution, but that has worked for me in the past.