Gearbox is the patch editor - you CAN use podfarm to edit you patches however it wont work as a standalone program on your computer. By that I mean that you need to use a DAW (Digital Audio Workstation) such as Cubase, Reaper etc. (there are many others). Podfarm is a .vst plugin so the DAW that you use must be able to handle .vst.
Many people have their preferences, some prefer gearbox some prefer podfarm (for what it is worth I personally prefer gearbox - although podfarm looks nicer).
Gearbox will work as a standalone program - in as much that you don't need to have it working as a plugin for a DAW. However you still must have your X3L connected, so in answer to your other question, no you cant develop a tone and preview it without your X3L connected with either pieces of software. Your X3L essentially acts as a security dongle proving your entitlement to use the software.
If you absolutely want to create stuff without the X3L connected there is a version of PodFarm (podfarm 2.5) that will work without the X3L however this isn't free and also the tones that you create with PodFarm 2.5 (or even Podfarm 2 for that) aren't directly compatible with your X3L. This is due to the way that PodFarm 2 / 2.5 route the different effects is different to how it is on the X3L.
Good Luck with all of this - it is great fun and feel free to come back and ask more questions.