Hey David,
I am no expert by any means but I usually take an incremental approach when adjusting resources...I will usually slice off a percentage at time, re-analyze then adjust further. Make sure you take into account spikes of activity to ensure you do not create constrains.
My personal experience, we initially set up the analytics vm with 6 GB of RAM until we went over the 1500 vm threshold, then we adjusted to 9 GB of RAM. We did not see any user experience degredation.
Good luck!