time for a new computer..desktop or laptop?

I do Sonar for fun but I'm semi retired and have lots of time for it and I'm determined to get good at it over time. 
I'm a Guitar/Singer/songwriter doing mostly audio now but looking towards midi as I learn. I also use a CAD program (Softplan) for my work (home design) which simply needs CPU power and a decent graphics card.

My desktop is dying as I write but I'm so confused about what to buy due to the rapid changes in IT.
Tho it's a couple of years old my Asus laptop is powerful enough to run my CAD 
(Intel Duo T660 CPU, 500GB HD, 4GB memory, win 7, Nvidia geforce G102M) 
and maybe I could get another one for Sonar alone?

If a desktop is better for whatever reason, can they be really quiet? Even with the good fans I can hear it in the mics. (same room) 

What ports would be wise to include? (I hear lots of good things about larger SSD's now)
My controller (BR800) with external sound card seems fine as an interface but does not have MIDI. I'll get a keyboard for that.
I guess the bottom line is:
Is there a good basic computer shopping check list available for sonar?