Long story short: an extra maintenance cart, a black cart (or matt black) and a set of the Lt. carts... I outgrew my 2200, then went to a 4000. We put in cabinets in the studio with that size in mind. The next year it was a 7600 and 24 inch cabinets for prints and sheets and little room to spare...now I have a 9800 and 9900 and run them both. Thought that 24 inch would do, but now find that for canvas, 24 isn't. Wish I had just gone large from the git-go and had been done with it!
I was lucky with my 9900 and found a second-hand unit about a three-hour drive. It's probably the best printer I've used, but any time you let it sit, you need to run a nozzle check to make sure it's going fine.
For the most part, the 350ml carts work well, not too large and expensive and they seem to keep going quite a while after the low-ink warning starts flashing, especially the Cyan cart, just like the rest of my printers. Cyan and MK are the ones that seem to last the longest followed by Cyan on my printers. On the 9900, the Orange and Green also last quite a while. The Light Blacks and both Light Cyan and Light Magenta go quickly.
If you can get your ink in a couple of days and don't print quite a bit, order as you need it, or start stockpiling as you watch the ink gauge drop.
Try the canned profiles since they are pretty good, but if you start using other surfaces, you may want to have at least a Colormunki to profile the different papers and keep your monitor in check.
You probably will be fine with the built-in cutter and won't need to change it for awhile. I've used mine for nearly a year now and have run several hundred canvas prints through it with no problem.
Black switch-over from PK to MK goes pretty quickly and easily. Best bet if you need to run each is to batch them to save time, space in the waste tank and, of course, ink.
Though I originally bought the 24 inch 7600 was simply for my own amusement, it didn't take long until others wanted me to print there work and it more than paid for itself and I found that it wasn't large enough. If you have the room and you think that in the next two-three years you need/want to print larger, then it may be a good idea to bite the bullet and go to the 44 inch. You can always print smaller. If you are like me and stumble into canvas printing, its the minimum machine you'll need.