Studio computer question

Hi.  I currently have Sonar Cakewalk X3 Producer, and will probably upgrade/update to lifetime updates soon.  I also have a Scarlett 18i8 audio interface, though I haven't used it much (so would welcome any tips in that area as well).
 
I'm going to be recording a weekly 1-2 hour show, often with a skype guest, and one or two people in the studio, filmed against a greenscreen.  i will also record music in the studio on occasion - mostly myself on an electronic keyboard with midi output, though may record kids and friends who use a mix of electronic and acoustic instruments.
 
I've been trying to decide between getting a laptop or a desktop for the studio, but am leaning towards a desktop since that generally gets more bang for the buck.  And if I get a desktop, trying to decide whether or not to get a silent, possibly fanless system, or just a regular box with large, slow fans, and an SSD drive to cut down on hard drive noise.
 
I don't have a specific budget.  Cheaper is certainly preferable, but I am hoping to do this long term in a fairly professional manner, and I've already invested in the audio interface, a camera, and an external recorder for the video, so it really comes down to weighing the benefits against the cost.
 
My external recorder does accept two XLR inputs, and I have a couple of okay condenser microphones.  (Have held off on getting wireless lavalier mics owing to cost - and open to suggestions on that as well).
 
Thanks for any advice,
Rob

Hi.  Home studio is roughly 21' long, 13' wide, and 8.5' high.  Has sound panels on three walls (not on the 13' greenscreen area) and on the ceiling above the area I'd use as my listening point about 40% down the room.
 
I do not have a separate control room.  Nor do I have a practical way to put whatever computer setup I use outside of the studio.  (I suppose I could drill through the drywall & the cinderblock between my studio and the basement room it comes off of and run cables for a monitor and keyboard through the wall)  But for convenience, I was trying to get a quiet computer that I could simply have in the studio with me.
 
Piano would be recorded as MIDI, but often will be accompanied by vocals - and will be some acoustic instruments as well.
 
I've thought about wired lav mics, and maybe that would be the way to go.  I'm trying to build in some flexibility, because I also put on and record educational programs outside of my home - hence the fleeting thought of getting a laptop that could do double duty.  But my main focus is on the home studio, and I'd rather be set up well for that, than having an okay setup for both home and traveling.