I'd highly recommend Micron Pigment Pens. They're incredibly awesome. I use them for all of my inks. Brush pens are also pretty sick for various effects. You just need patience and a steady hand. It's a lot like lineart when painting digitally.
No tool will help you work better with ink. If you are really good, you could go about using childrens' ink-pens(Though I do not recommend it). Learn to be light on the hand, using quick but carefull strokes. But as with all creative learning, repetition is key.
There is no best size and brand of pen. Use whatever helps you specifically to get the look you specifically want using methods that you specifically enjoy. That means you'll have to try different things. You ink them your drawings by first creating a relatively clean drawing in graphite. Then you trace over the lines in ink. Then you finish erasing the graphite. If you use non-repro colours to sketch and intend to colour either digitally or over a printed copy of your work, then you can save all the cleaning for after you've scanned.
An inker is an artist who's job is to complete the pencil drawing in ink. This often means enhancement or elaboration of some kind. The position was created exclusively in the comic book industry early in the 20th Century since it was essential for the work to be in ink when printed back then and for the sake of expediting the production of comic books and allowing popular pencil artists to handle more titles, this increasing the publisher's bottom line.
Depends entirely on the style you want to achieve. Different inkers can make the same persons pencils look completely different - compare McNiven's pencils (inked by himself, as far as I can find) in Nemesis vs his pencils (inked by Dexter Vines) in Old Man Logan. Decide what look you want to go for, study things that have that look and figure out what they did and what tools you'll need to get it.
There are many different ways to ink your drawings and one persons preferences can be another persons dislike. The trick is to try as many different ways as possible until you find the one you prefer (and even then try new ways). At the moment, I scan my pencil sketches into my computer and print them out in blue, then ink them with my Fiber-Castell PITT artist pens, which are a set of four ranging from XS to B, then remove the blue in the computer.
I find this technique beneficial for me because, 1) if I make a mistake on the ink, I can reprint the sketch and 2) I don't have to worry about erased pencil marks showing through on the scan.
Try starting with a 0.7 to 1.0 (might be labelled as 'F'), they are the closest size to the everyday ball pen. Once you are used to that, start using the smaller one for fine details and the brush pen for the thick lines.
I've been experimenting with pen size lately so feel free to look at the recent artwork in my gallery.