I always thought Rng was a good in-between for mages, since they are more of a hands-off job, but melee non-the-less. It gives you opprotunities to try things like Engauging the mobs(Pulling) and Finding out about links and what not. It also is not the most heavily armored job of the lot, which you are use to, but will teach you the harsh realities of being melee...
Path eto Ranger:
Take Monk to 5
Take Warrior to 10(Subbing Monk)
Take Nin to 20(Subbing War)
Take Ranger to 40(Subbing Nin)
By the time you do all of th eabove you should have a better understanding on how Melee jobs work, and can be in pretty good standing to go back and double the levels of each job(Rng to 75 not 80).
Monk as a precurser, set you in the mood, a kinda Hands on approach, nothing complex about it, just hit attack and go...
War, get minor tanking duties, Learn to and when to provoke.
Nin, bring in finese of the Melee jobs. It doesn't really shine till you are about lvl 40 or so, but it's still a good job to 20. Problems with Nin only arise with Party Dynamics between 24-32.
Ranger, Pretty self Explainatory, You basically have a really advanced version of 'Gil Toss' you throw your Money at a mob in the form of Arrows and Get a lot of invites...
Once you get Nin to 20, you can take most other Melee jobs to 41. Once you get War to 37 you can take Nin to 37+ and with either of those two subs, you can take any Melee job all the way successfully.
The trick is to keep your Subs leveled before hand. Less interuption and consistant gaming.