Just list ssids along with size, sort it by size and then select ssids as per any criteria you want.

I have a script working that will get the list of savesets and total up the sizes up to the amount I want to stage, 3T, and send them to nsrstage but I'm having a heck of a time getting nsrstage to redirect output to a file to check for errors or even email the output.

I've tried stdout/stderr redirect, tee and script..... Is there something special about this binary.....

(and you can use similar trick as described in Crazy little thing called nsrsgrpcomp if it is stubborn...)

For staging you should also use nsrclone (nsrclone -m).  You can direct output (there are couple of binaries which require some forcing, but as far as I remember nsrclone is not one of them).