There is lots of good advice above. Here is my take on your questions:
Simplest and Easiest Pen Kit:
Like others, I think that the single tube pen kits mentioned by others (Sierra, Wallstreet II, Gatsby, Manhattan, etc.) are the easiest to make. On the other hand, the slimline types cost half as much, and you get to turn two separate blanks and assemble them together. Both types of pen kit are forgiving if you cut off slightly too much when trimming/squaring the blanks.
Personally, I would recommend that beginners start with slimline type kits, the cheapest ones available. They take a little more practice to get right, but once you have mastered them, you have mastered many useful skills. (Not much more effort, honestly.) In my opinion, your resulting skill level will be higher than with the single tube pens.
My second choice would be the second least expensive slimline type kit. Why spend the extra money to learn the craft?
(If you must have instant gratification with pens that will impress your family and friends, the fastest way to that would be those single tube pens. They look really good and professional, but much of the "impress" comes from the kit parts and the fact that
you made it, in my opinion.)
Where to Buy Kits:
I prefer to buy pen kits at a local Rockler woodworking store, to save on shipping costs. I have ordered from Penn State, but only because many of their kits are sold at my local Rockler store. Sometimes I need a matching pencil kit or a different plating that is not available from Rockler, so I am forced to go to Penn State. Penn State has good people and good support and lots to choose from, but their pen kits are mediocre.
You live in Mission, TX, far from a well-stocked woodworking store, so mail order is your only choice.
-> Start with Exotic Blanks
https://www.exoticblanks.com
What Materials for Learning and Making the First Few Pens:
Yes, wood is best. I always recommend that beginners start with wood. Avoid softwoods like pine and fir.
To make your own blanks, take any board and cut out pieces approximately 3/4 x 3/4 x 5 (or 6) inches. If you are using green (fresh) wood, cut the blank to size, and then let it dry thoroughly for a few months.
(I have made pens from down branches. They look good to start, but you can turn off all the pretty wood and leave only a bland core for your pen. I do better with pen blanks cut from the ends of boards that were bought for other woodworking projects.)
Not Asked: What Single Recommendation Do You Have for a Beginner?
Whichever pen kits you buy, get spare brass pen tubes for it. They are cheap. If something goes wrong, you can still use the pen kit. Just start over with a fresh pen blank and a spare pen tube. Having spare tubes on hand takes so much stress out of pen making, when it is easy to experiment or replace errors, without wasting the pen kit.
You can still damage pen kits during final assembly, but until then - drilling, gluing, milling/squaring, turning, finishing - if you ruin the project, you can easily start over with the same kit. That takes away many of the concerns that beginners can feel.
