Core i5/7 15" MBP
I was in a similar position 3 years ago, (although I was running mostly chem/bio apps and DV/Photoshoping was a job not major.) I went for the fastest portable mac I could afford, with the nicest screen I could afford: the 15" MBP Matte Display, and I haven't regretted it once.
Eventually I added an inexpensive ($~180) Dell S-Ips display (2209WA) which has worked wonderfully for editing and as additional real estate, and a FW 800 External (which I built very easily from an enclosure and drive, ~$140, probably less now) and some portable, bus-powered 500GB 2.5" FW400 drives for field work. So basically I have a 3TB 20"+15" setup that is completely mobile and that has multiple HDDs for data redundancy (My photos are routinely backed up on at least 2 externals plus a lower-quality web-sync, i.e. Picasa).
So, as a student, I would spring for the best Macbook you can afford right now, and then build your setup, adding new, highquality components when you can afford them and as you need them.
I wouldn't get a desktop, though, since I have found numerous uses for my Macbook out in the field, (class notes, last minute papers, international trips, mobile video recording/editing/field monitor, VOIP, ect.)
Personally, I don't like the new Imacs, as their display is too glossy and glare-prone for true color representation and extended work (not to flame, this is obviously my opinion, having originally edited on Sony Tritons back in the late 90's, and Dell IPS displays since) and they are bulky, and not as upgradable as, say a used Mac Pro, which would be the only other thing I would consider for semi-pro work (since you could hook up 2 20"+ displays).
So my vote: 15" iCore7 Macbook Pro Matte if you can afford it. H3ll, 17" Macbook Pro i7 Matte if you have enough $$. (I'm guessing, from my grad student perspective, no!)
Good luck on your studies!!