@thorns Tools and systems are both beloved to those in the fountain pen community and we can talk for hours about them! I would like to have the kind of life that's conducive to writing out all my lists in fountain pen. However, I have a lot of moving parts to deal with in my recent projects, so I need to use software to keep plates in the air (Amazing Marvin and Basecamp).
However, I do use paper for most of my actual working through things.
My best advice for buying fountain pens is to find an actual brisk-and-morter pen store and try some there. Everyone has their own tastes, and it's better to figure out that it's not a good fit in the store rather than buying lots of stuff and not using it.
The Kaweco Sport is one of the best pens to use for both beginners and experienced users. TWSBI also has many different filling systems and nibs and are relatively inexpensive. It's worthwhile figuring out what your tastes are before moving on into the serious rabbit holes such as Montblanc, Pelikan, or the endless rabbit hole of vintage pens.
I'm glad that you made the bullet journal method viable! I really wish I could. However, the type of work that I do requires me to be at the computer more time than not, with lots of quick entry needed. Maybe once things slow down a bit...