using keyboard for piano and virtual instruments?

Hi guys,

Total noob here :)

Here's what I'm trying to do, and I can use some advice on how to pull this off (or if it's even possible).

I'm using Cubase Essentials
a Roland keyboard/digital piano
EZ Drummer (drum virtual instrument)
Motu Symphonic (orchestral virtual instrument)
Presonus Audiobox USB sound interface

My setup is:
I have the keyboard connected to the presonus box both through midi in & out, as well as through the keyboard's "line out".

*whew* ok, now here's what I'm trying to do: I'm trying to put together a track that has, say, a piano track (using the sounds that the keyboard has), plus some symphonic and drum tracks using the virtual instruments.

I'm thinking that I ought to record the piano track in MIDI rather than just using the raw "line out" sound since then it would be easier to edit later if I needed to. But then if I did it that way, would it be possible to use the keyboard to record the other virtual instrument tracks? I'm imagining that the keyboard would be tied up supplying the piano samples when recording those other track, although I'm probably just confused :)

thanks in advance for any helpful advice.