Hey Micah. Playing as Drk/War so far, I can maybe offer some insight atleast from my own experiences.
Since Darkenatrocity answer most of your questions pretty much already. The only thing I can really focus on is my experience with keeping my weapon skills capped.
I didn't have to worry about leveling greatsword much as a Drk because when I went through playing Warrior (first job) I used great sword as my weapon and capped it at lvl 40 on Warrior which was like 120something I think. This allowed me to simply focus on Scythe as an early Dark Knight and pretty much didnt have to worry about my Great Sword skill up untill the last 30's. Once Great Sword was no longer capped continued to skill up and cap Scythe every level, once scythe was capped I switched to greatsword for the remainder of the level (which usually wasn't much longer).
I focused mainly on making sure to always cap my scythe, because scythe's are the most damaging weapons in the game (having the highest dmg rating). There were a few levels in the late 40's that it became hard to keep scythe skilled, but that was mostly because I was making my own really great parties and zooming through exp, not nessicarily skilling up my scythe as much. Though in the in the early 50's scythe got back to being capped, and by this point it was far ahead of greatsword by like 40 points. At this point, it was nearly impossible to try and skill up greatsword in a party because of the frequent misses.
At about lvl 54 or 55 I went out to altepa, the zone that connects east and west altepa dessert, and I dont remember which side exactly it was, but I skilled up on the beetles. It was slow going, pulled with abs-vit I think (this was some time ago), might have been abs-mnd then abs-vit, and just fought near the zone line. Even at that level those beetles are EP to EM, good enough for skilling up, but you can be killed if your not careful. to prolong the fights a tiny bit gotta make sure to aspir/drain, but if your hp gets to yellow that's when its time to stun and zone. Doing this i raised my skill about 10 levels in a few days but then it seemed to slow down quite a noticable bit. So I asked a 60+ whm friend to come and help me skillup one night. When he came, we fought some DC-T Anticans that raised my skill up more, but still didnt cap it, I ended up being about 7 points away from the cap though which wasnt bad at all.
From then I was able to use my greatsword in parties (after i had already capped my scythe) and at lvl 56 I finally managed to cap Great Sword skill as well as my Scythe. Now with the TNL I have and the accuracy gear I have, I dont think it's really going to be a problem at all keeping both capped from now on. I'm able to have scythe capped by about 5k-7k exp into a level, and at 20k tnl, that 13kish exp left is more than enough to get Great Sword capped and switch back to Scythe before the level is up. Just make sure your able to find a good switch in the skillchains. There usually is a Great Sword WS that can replace the Scythe WS you were using and still maintain the same skillchain. It all depends on the skillchain though. Sometimes you may have to workout one ahead of time. And let the party know the new one, if the order of the WS's they need to use is different.
I hope that helps somewhat.
