[Numachida]

"Would the ProTools/Cubase combo work on the same PC?
In other words...Run Cubase and do my sequencing then save sequence to .MID file then close Cubase then Run PT and import?"

Yes-but I don't think that will solve the softsynth issue. Some users print their seq's as audio and import the audio into Protools. If you've already got Cubase that 2nd PC would't be much of an expense and Cubase doesn't require nearly the power to run as Protools.

"Lastly...I have crazy latency when playing soft synths into PT and/or Cubase? What gives? I must be doing something wrong. How does one resolve this issue?"

Haven't ever used a softsynth in Protools. In Cubase you have to tweek the audio setup a little-I don't remember where exactly, but you can reduce that latency to the point that it's undetectable.