I agree with most of what said above. But I'd spend a week or more reading & re-reading information in the library. Not just the beginner section, but anything that you find interesting. That's what I did before I ever ordered anything. And it saved me a bunch of time, frustration & most important, money.
One thing I decided to do was to turn between centers. I never bought a pen mandrel. I kept reading about blanks that were out of round, or mandrels that were not true when new. At first it seemed that only experienced turners didn't use pen mandrels, so I assumed it took more skill. In fact it's just as easy, and some things are easier.
Another thing I decided to do was to drill on the lathe vrs buying a vice for pen drilling. I do have a bench top drill press, but I've drilled a few pens on it with an improvised setup till my collet chuck arrived.
I agree that a sierra style pen is a great 1st pen. It's easy to make, and you can fix it if it has a problem. This was one thing I did wrong. I started with slimlines. I bought about 20 thinking it would be good practice. After 3 I was ready to try new things. So only buy a few of whatever you want to try 1st. Or maybe a couple of a few different styles. Don't go crazy buying kits till you get a few under your belt.
One other thing to do is to read the kit evaluations under "Product Testing and Review".