I think I've heard something about these dip nib things.
Welcome to the wonderful world of "how we all wrote for a hundred years!"
Others have gives some good advice and encouragement, so some of this may be duplication, but I thought I'd tackle your list of questions. Obviously, these are my own opinions, some are shared and some are not, but there you are.
1) Is there a Dip Pen Network? (google failed me here).
Alas, no. The Flourish Forum was suggested, and it's an amazing resource if you're interested in calligraphy of any type. A great group of folks there, but there's limited interest in history or every-day kind of writing. They do have great advice for inks, and paper, and of course, the beautiful calligraphy, as has already been mentioned. I look for the occasional dip pen topic here, or you are welcome to bring up any questions, comments or suggestions in this general forum, which is "Fountain and Dip Pens" after all.
2) Is ebay the best place to find these nibs?
I find most of mine there, and there seems to be a good supply of general-purpose vintage nibs still available. Look around for a while to get an idea of what is there and what people charge. If you want to buy individual nibs, especially if you want to explore different types (and there were thousands of different types from many hundreds of brands), Pendemonium
is a good place to pick up a variety. (no connection, just satisfied customer). I've had much less success finding the nibs in antique stores. Every once in a while I'll run across a box, but some people have the idea that because the nibs may sell for $1-$2 each when sold individually, that they should then cost $144 for a gross box. Actually, a box of common pens (not the so-called "dream pens" so desired by the calligraphers) should sell for $20-$30 or so, plus or minus $10 depending on rarity or condition. Don't pay $80 for a box of Esterbrook 048 Falcons, even if it's sealed. They made hundreds of millions of them and many are still around.
3) Dip pen holders all seem pretty basic. Are there differences between them that I would notice?
Straight holders, which I'm assuming you're talking about, vary by material and holding method (the mechanism which holds the nib in the holder). The modern, manufactured ones are inexpensive and work for the majority of nibs. There are some vintage nibs which are a bit too wide for modern inserts. This is where vintage holders can really come into their own. Eagle made a good, school holder which I see all the time for sale. If you're going to buy vintage, unless it's an amazing material, don't buy it unless you can see the holding mechanism. You have to make sure it's not rusted. Some dipped their pens too deeply and got that steel insert wet, and it rusted. If so, the holder could be useless. Keep an eye out for some of the really fun holders like the celluloid, agate or glass holders. Some are expensive, but most are fairly moderate.
4) My Esterbrook 442 nibs dropped a pretty wet line. Is that typical? Or do I just need to learn better control?
Dip pens, in general, lay down a much wetter line than a fountain pen. That said, if the nib is not properly prepped, the ink will slide off much more quickly than you want. I have some suggestions
on my site on how to prep a nib. (there are other suggestions
for getting started there as well.) The 442 is a stub pen and will lay down a thicker line, but the wetness of the line is a factor of pen, ink and paper. (just like fountain pens) I like to use 25% cotton laser jet paper for most of my writing. I will print out lined paper, practice sheets if I feel ambitious, or just go freestyle if I'm feeling adventurous. The Black & Red notebooks found in most office supply stores also has excellent paper for dip pens. The rest is up to the ink. (see my ink answer below)
5) My collection of Fountain Pen ink is surprisingly incapable in dip pens. It as though the formulations for modern ink are such that they "expect" to be flowing through a feed unit. Some of them just could not stick to the dip pens nibs (Kiowa Pecan, I'm talking about YOU). Is this typical behavior and, if so, what inks do work best in dip pens?
As others have pointed out, some fountain pen ink works well with a dip pen, others don't. Some, counter-intuitively, work "drier" if you cut with water. Monteverde inks work quite well if you dilute 1:1 with water. Pelikan 4001 ink works quite well with dip pens straight out of the bottle, as will most iron gall inks. (super-saturated iron gall inks may need to be cut a bit as they can add a lot of lubricants which make it slide off the pen a bit too well)
My favorite ink for practice and some letter writing is what is often called "walnut ink." I prefer the crystals because you can buy a bag of a few ounces of crystals for not much money and it will last you for months of regular writing. You can also dilute in water to the preferred depth of brown you want. I've used them for years now and use this ink whenever I give a demonstration or let others try writing. You can get these crystals from pen in ink arts, mentioned by another poster, or from John Neal Booksellers, who I tend to buy from because they're just a bit down the road from me.
Here's an example of my every-day writing using walnut ink. (four years ago I didn't really know how to write cursive, but dip pens got me so motivated to re-learn, I now have a decent hand, though not a patch on the real calligraphers)
If you start to get interested in the vintage nibs and where they came from, my site also has a fair amount of history on it as well. I'm only up to about 1880, and there is so much more to tell, but I've gotten a bit bogged down turning some of my early posts into actual articles published in The Pennant, the magazine for the Pen Collectors of America
Again, welcome to dip pens. It's an interesting world with so much variety to choose from. Each pen has its own "experience" and if you learn to have that light touch, also mentioned above, and use the right ink and paper, it can be so rewarding and just plain fun.