Ipe makes a very nice pen. I have made several, one is a worn out slimline I made a few years ago, one of the first pens I ever made, and the wood is still great. However, it WILL stain if you don't put a good oil finish on it (this is about the only wood I'd use an oil finish on for pens).
1) Cut your pen blanks, bring them into the nice, dry house, and forget them for a month, at least. Ipe is almost always milled up for *exterior* use and not always kiln dried to proper moisture content since exterior stuff doesn't need to be. If you don't let them "dry out" some more, you run a huge risk of the pen cracking.
2) Sharp tools are necessary, but turning the stuff really isn't hard at all. It cuts great for me.
3) Do NOT build up a lot of heat when sanding, or you again run the huge risk of the pen cracking (even later on after it's sanded). BTW, Ipe is a brown wood, but the bright green sanding dust is just plain weird. I've never seen wood do that before.
4) If you decide to make furniture out of your lumber stock, just know that Ipe HAS A HORRIBLE reputation for not being wood-glue friendly. The joint will only last long enough for you to like your furniture, and then the joint fails. I don't care what solvent you clean it with, what kind of saw blade or jointer you used for the glue joints, what kind of wood glue/PVA glue/Resorcinol glue/epoxy you use. Ipe is just too dense for glue to be effective. Use lots of screws!