I Started years ago with an M audio fastrack pro for audio & midi I/O, then upgraded to a Focusrite saffire pro 40, now I have this Presonus 24.4.2 for audio but no midi.... Can I plug in the ole' fastrack pro via USB just for the midi I/O portion of it?  I haven't tried this yet as it's up in the attic! 

Shouldn't be any problem.

I have some MIDI/USB issues on the list to work out.
 
Running an M-Audio 2626 Profire, with 2 ADA-8000s slaved via Toslink, and an M-Audio FTU slaved via SPDIF, for 26x26 I/O, (or 32x32 w an 8x2 submix), which gives me one MIDI I/O on the 2626, via Firewire. The FTU is USB hosted on a second PC.
 
In addition, I use an M-Audio Midisport 4x4 on the primary DAW, via USB,  which coexists peacefully with the 2626, however...
 
When I connect a Korg, Nano2 control surface to that same machine via USB, the Midisport 4x4 disappears from the MIDI options list in Sonar, even though Windows Device Manager shows all three MIDI devices (total of 6, Profire, 4 Sports, and the Nano) working perfectly.
 
Current workaround was to unplug the USB Nano, reinstall the Sports drivers, and it reappeared in Sonar.
 
Not saying the combination is unworkable, cuz I haven't dug into it, just that the second USB/MIDI device caused problems, while the MIDI/FW and single MIDI/USB devices do not.
 
You might want to take care opening lots of projects while testing out 2 MIDI/USB devices, or any combination of multiple MIDI ports, really, cuz Sonar is going to want to reassign MIDI port routings when/if the originals become unavailable. A test project created for the purpose should avoid this problem.

I appreciate the heads up bud.  I do almost zero midi anymore.  I used to use a roland V-kit and track the drums midi, and had a kyeboard part in a song or two a couple of years back... but I had a few bands pass on using me because of the electronic drum kit scaring their drummer off, So I sold it and bought a nice little acoustic kit for the studio.   I don't have any midi tracks at all in any off the songs I have done myself or even done for other bands in the past year.  I just want to make sure I CAN if it becomes needed for a project in the future.