A whole world of opportunity opening up here!
There's a pretty good fountain pen forum at
http://www.fountainpennetwork.com/forum/ full of tests of pens, papers and inks, with comparisons, side by side ink stuff, detail on pens you've never heard of. If we can be called WIS, they unfortunately are PIS.
All the stuff noted above is right. For amusement, I've bought all but one fountain pen second hand (up to 5 now), and they've all been fine - a Visconti Homo Sapiens Bronze arrived while I was away this week, with something called a stub nib ( a rounded version of italic) which I've been using this morning; mad pen, lovely line.
The whole paper and ink stuff will get you as well. Starting with just the usual bottle of Parker blue, I've now got of reds, greys, ambers and greens, with a pen for each colour (see, started easily, went mad. Sounds familiar, doesn't it).
Papers a nightmare too. Notepads, sketch weights, I'm now using a notebook made by a bible manufacturer - incredible thin paper with no feathering or bleed. (Don't ask..)
Pen cases, pen rolls, travelling inkwells, it's endless. It's cheaper than watches, but I do occasionally think it's even madder.
Hey ho, keeps me off the streets.