Just a few random thoughts for the beginning fountain pen turner. Almost all the FP kits available now are also available as a rollerball kit the only difference is which section is supplied (oh, and the rb kits come with a spring, fp's don't). Most threads are identical enough to freely swap back and forth from a rb section to a fp section at will. Thus "turning" a fp is no different than an rollerball.
Which kit should you turn? Depends on what you can afford to spend, vs what you want. You can get fp kits anywhere from $6 each to around $100. My personal favorite is the Jr. Gent. It comes in all the best platings, it has nice metal to nylon threads in the cap, the threads are plated to match the rest of the kit instead of being black enamel (except for the low end gold kit) so they won't wear through. You can get spare tubes for them easily, (including colored ones less likely to show through plastic blanks). It also ALWAYS comes with a plated metal front section, with a separate plastic holder that threads in to hold the nib and feed.
Some kits use a one piece all plastic section to hold the nib and feed, and I have had several problems with these, both breakage, and not holding the nib and feed well enough for the ink to feed well. Now some of them are fine, but why take the chance if you don't have to. I ALWAYS ask a vendor if the sections are all plastic before I order.
Most people start out with the jr size pens just because of the price of kits, and the drill bits needed for them. However, I have found that the larger full size gent pens are usually less prone to problems with the fountain pen sections, are more comfortable (for me) to write with and are easier to turn because the finished material around the tube is a little thicker. They are not light to carry around in your shirt pocket though.
