Canon printers don't clog often (or better they can isolate clogged nozzles), although the longer you don't print, the higher the risk. Still, if you buy a printer, you're going to print, aren't you? It is true not printing often may mean some ink is wasted (cleaning cycles and so on), so you'll end to spend a little more. You may just print some small 4x6 prints, or even a small stripe, to keep the printing head healthy.
Sure, you need to learn what you're doing - especially how to manage a "color workflow" properly (even if you print B/W, eh eh), and you'll need to calibrate and profile, so you'll need the proper device as well. You do it if you want to manage the whole process from capture to print, and print exactly the way you want (it takes some time to learn...). You can print at the sizes you like (within the printer limitations), using the papers you like.
You don't do it to save, though, it's not cheap, especially if you use high-end papers.
Depends on the printer technology and, if used, inks. The Pixma Pro 100 uses dye inks, the 10, 1 and beyond use pigments. The latter should last longer - but a lot depend on what paper - and how it is manufactured - is used, how the print is mounted or stored, where it is placed, etc. etc. Some printing shop may still use inkjet printers and inks very similar, and cheap ones maybe inferior ones. Other technologies may last more ore less.
This people (
http://www.wilhelm-research.com/) do a lot of testing - just they are accelerated testing so they can't give specific data for a specific situation.
Keith Cooper (
http://www.northlight-images.co.uk/photography-articles-and-reviews/printing-paper-reviews-articles/) has written some very useful articles about printing and color management, he's also a Canon Rumors member.
If you're interested, at that price you can get an entry-level pro printer which can give far better result than most more consumer-oriented printers, and see if printing is for you.
Now I have to print on my Pixma Pro 10....