Allow me to try and explain based on my understanding. If there are technical points described without complete accuracy someone with better familiarity will need to correct me. I can resolve the notification issue however.
LMCE does not keep media partitions mounted. Part of the radar that detects new drives does an occasional /mount (performs checks?) and then /umount. So far as I understand it, you may test to verify, a partition needs to be mounted in order for xine/mplayer to read from it. While doing playback of a movie known to exist on that drive do you still see the notice every 15 minutes?
To change notifications for individual orbiters, there is a setting in webadmin>orbiters>advanced which from memory is simply called "notifications." There are no tips for this input to display all options but choices I have discovered are:
-I assume there is a null/0/none/off setting but I haven't found it.
On my WebDT, weborbiter2 devices and theater setting on-screen orbiters I use "important" though a zero setting would be ideal. For the onscreen orbiter of my hybrid (which is a 23" desktop monitor) I prefer the all setting as I am kept up on system workings, the downloading of new packages etc, when I am presumably more able/willing to make corrections or adjustments if necessary.
*I reread your post and wanted to ask specifically how you told LMCE to use the 1.83TB(-install size). Most of my core setups have used smaller disks for boot/OS and larger disks for media. I may again be wrong but my understanding here is that "all on one drive" setups would bottleneck streaming content to MDs while trying to copy a DVD on another MD and manage database read/writes all at the same time.