You and I are very similar: I've been a professional print designer for 20+ years. I work on high-end publication design: A lot of niche magazines, book covers, etc. I use a 2013 iMac as my primary work machine, having upgraded from a 2009 iMac (both 27"). I use Photoshop, InDesign, and Illustrator 90% of the time (CS6). I can share my experiences, although realize this is just my experience. Others may disagree.
1. My 2009 had an i5, as does my 2013 (3.4GHz version). None of the software you mention will materially benefit from an i7, especially if your budget is limited. It's not worth the $200 expense. Note I say materially. The i7 Apple offers is clocked slightly faster than the i5, so there is some difference, I just don't think it's $200 worth of difference for the software we use. The i7's primary benefit comes from the eight virtual cores made possible by HyperThreading, which won't benefit the software you mention to any great degree. The four real cores of the i5 offers more than enough threading potential for the limited ways ID/IL/PS take advantage of it.
2. Don't bother with the upgraded video card. Of the software you mention, only Photoshop offloads work onto the GPU, and even the lowest-end dedicated GPU has more than enough horsepower for this purpose. One thing to consider is if you might want to add a second (or third!) monitor in the future. If so, more VRAM will help—choosing the higher-end iMac with the 2GB option will buy you some headroom. The only reason to upgrade the GPU is for games or if you anticipate pushing hard into 3D modeling at some point in the future.
3. I don't have any experience with the Fusion drive so I can't directly compare it to a pure SSD solution. For my 2013 iMac, I went with the 512GB SSD and can say it's been the greatest single improvement over my 2009 iMac. I keep all of my immediate "in process" work files on it, and everything absolutely flies. PSD files—even giant ones with dozens of layers—pop open in Photoshop like nothing. Similar with complex InDesign files. My goal in getting the SSD was to be rid of internal spinny disks. I wanted my machine to be as quiet and reliable as possible.
Using the SSD does require me to manually manage files between my external storage (6TB of archives, client files, raw media, etc.) and the SSD, but I like having that control. I would rather be able to exactly dictate what goes where and what I want to have on the SSD for immediate access. I haven't found that process to be problematic. I went with the 512GB SSD, despite the cost, because I knew it would give me plenty of space to hold all of my in-process files, plus applications, plus the system, with room leftover. The 256GB SSD would not have, and certainly the 12GB SSD that makes up part of the Fusion system wouldn't be enough. I'd have ended up hitting the regular hard disk way too often for my liking.
Finally, and this goes for any system you buy: memory, memory, memory. I have 24GB in my 2013, up from 16GB in my 2009. I regularly hit swap in my 2009. 24GB has bought me some headroom, although I'll likely max it out to 32GB before too long. Anything you can do to avoid swapping will keep the software you use speedy. Photoshop performance in particular degrades tremendously if it can't allocate enough memory. But this will depend on the size and complexity of the files you work on—print imagery is (of course) significantly larger and requires more resources than imagery for the web.
Hope this helps.