MIDI track troubles

[gonedigital]

Hi everyone,
Hopefully someone can help with a few problems i am having.

I have a resonably good home PC and i use a Tapco USB interface for my recordings.

I have about 24ms latency in my system, which i get around when recording live instruments and vocals by setting the 24ms as a delay in my software on each audio track (i use Cubase SX3)

Is this 24ms typical or is a lower number what i should be looking for.

The main problem i have at the moment is with VST and MIDI.
I use a Berhinger USB MIDI keyboard, all is good when i put down the first track (lets say strings) i can set my "attack" and "decay" settings on the key board just the way i want but then when i lay down the next track and want to change the settings for shorter notes it still effects the previous tracks.

I have read the PDF docs from Cubase but just cant figure it out, is there an easy answer hopefully i am missing something basic.

Thanks.