Design my Computer... What Option Shall I do? iMac/MP Specs?

What about:
Macmini quad i7 (899$)
16GB RAM (150$)
2x256 Samsung 840 Pro SSD in raid 0 (460$ incl cable) for disk speeds above the MacPro PCI SSD!
Dell U3014 (2560x1600 AdobeRGB monitor with 3D lut) 1199$ (don't be skimpy on the screen)
And invest good in storage/backup, I have no suggestion for that, only 2700$ is spend and 2300 is left for your backup/storage/software needs.
Grabbing an iMac without SSD is really making that machine a horrible experience for video. Even more than RAM, fast disk access is needed, hence my suggestion of SSD Raid 0.

 

Skip for the moment the type of computer and look at your applications first.

See which ones are CPU intensive and which ones can take advantage of GPU (graphics processor(s). I mention this as you seem to have a good grasp at what applications you want to run and there are pluses and minuses with each of the options you mentioned (as well as the Mac Mini).

Mac Mini - limited to 16 gig RAM, on board Intel 4000 GPU.
iMac - good built in monitor but not 3rd party quality monitors are better for colour correction/calibration (NEC, Dell, Eizo etc.). Not so easy to swap out hard drive and replace with 3rd party SSD but can be done or to make a larger "fusion" drive set up.
Mac Pro - limited ability to upgrade internals at this time. GPU may not be suited for your apps. If able, consider the "sweet spot" of a 6 core with the D500.

I can't tell you what best fits your needs. I do believe any of them will work but some will be slower than others. If major speed is not an issue, the Mac Mini 2.6 quad is a nice place to start and a 3rd party monitor. I believe that a swap out of the regular drive for an SSD is far better than BTO SSD from Apple. Samsung EVO and Pro series are excellent choices for SSD. Caveat to striping two internal SSD in the Mini - if one fails you lose everything and thus back ups are absolutely vital on a frequent basis. Also if the "top" SSD fails of the two, you will have to entirely take apart the Mini again. (I speak from experience).

Summary - see what your applications exploit as far as CPU and GPU. Make a selection based on this and your budget. If you opt for 3rd party monitor, make sure to get one that calibrates well and is the appropriate size for your needs (not everyone is comfortable with 20", 24" or 27" so you need to pick what is easy for you to work with). Dell, NEC, Eizo to name a few make some models that are meant to be used for graphics and thus calibration to get the large gamut space is more likely.

 

It is now, but GPU support in applications is also sub-par right now. The solution does offer you to spend your remainder in cash on yearly hardware updates, and by starting with a modular system is wise in this profession.

 

I concur that the Mac Mini is not a "hero" in the forward hardware arena. However, spending over 2000 for an iMac that will also fall quickly (hardware-wise) behind is also a challenge.

For a modular system - go with building a PC and put another OS on it. Mac Mini, iMac and the new Mac (mini) Pro are not modular by nature but "extensions" from external devices add to the mix. Honestly, I think Apple would have been better positioned if they made the nMP with 1 graphics card, an additional "slot" that could either house a 2nd drive or another graphics card so people could adjust based on work needs. I opted not to get into the nMP venue (yet) given that the use of ATI GPU which gives me nothing x 2 for my apps. Oh well.

 

What's your timeframe like?

If possible, wait till the end of Feb to see if a new mini emerges. If it does, and it were to get Iris Pro graphics, I think you have your machine.

Speaking as a previous iMac owner, I would never buy one again. Too limited, too locked in.

The MP, although very very nice IMO, is a lot of cash, and a rev one product.

A new mini (hopefully with dual drives) is your best bet. Screen of your choice too. With any luck Apple will go 4k compatible on every model heading forward.

 

It's quite simple, actually:

SSD is really, really fast. And it's either small or bloody expensive.
Hard drive isn't very fast, but huge hard drives are really cheap.

Fusion combines both. It is very fast and huge while not that much more expensive than hard drive. It's like a small SSD plus a hard drive, but the Fusion drive optimises continuously what bits should go on the fast SSD and what bits should go on the slow hard drive, so it makes much better use of the space on the SSD than a human could, and you don't have to spend time doing it by hand.

Fusion is clever, but not magic. At some point it will run out of steam compared to an SSD drive. But as I said, big SSD drives are very expensive. And Fusion drive is _always_ faster than a hard drive.

3TB hard drive is a good idea especially for video data, even if you don't need all the space. Hard drives get slower as they get full. A full 1TB hard drive is a lot slower than a 3TB hard drive that is only one third full.

All in all, for the same money I'd switch to Fusion and take the 2nd fastest processor instead of the fastest one.