Massive keystroke lag and input latency. Help!

Thanks to your help, things are working well.  I still have some lag and that's to be expected.  I think I would like to add some ram so, could anybody tell me, given the info I have already posted above, how much RAM I would be able to add?  I've had issued in the past, trying to add too large an SD card and having the camera tell me it doesn't support it or, too much this or that in a computer and being told the motherboard doesn't support it. 

The only other question is, what is the empty slot shown on my motherboard for?

Thanks.