Welcome to Ragnarok, my fellow San d'Orian! If you ever need anything, I'm usually on my BLM, Tiffarah. Jus' a warning, even though she's a chick, I'm a guy. She's just a heck of a lot more fun to play and RP than my male characters. I also started her as a RDM. I lvled RDM to 20 and decided to start lvling BLM as a sub. I'm nearly to 20 on BLM as well. My WHM is only lvl 5 though, so if you ever want/need a healer, hit me up with a tell and I'll lvl WHM for a while.
I'm usually on from 6-9am PST on weekdays. It's early, I know, but I have no time in the evenings. I have managed to make quite a few friends from all over the world because of it, though. If you ever need food, I am a cook as well and can advise you on what food would be good for your job.
A few tips at early lvls... Always have signet cast on you. Enemies will drop crystals this way, which you can use for synthing or sell for profit in order to buy gear. It is probably the best moneymaker early on. At first, all you will get is Earth crystals in W.Ronfaur, from rabbits and worms. Occasionally a wind crystal from bats. But fear not, the days are coming when you will be able to kill orcs on a reliable basis. This nets you fire crystals. Depending on the economy at the time, fire crystals usually go for 4-5k a stack (12/stack), wind for 3-4k a stack, and earth usually hover around 1k a stack.
Be sure to pick the right weapon for your job. Each job has a weapon type they are most proficient in. At first, as a RDM you will likely go with swords, since you will be playing melee as well as spell casting. Later on you are going to want to switch to wands for the boosts they give to your magic skills, and because you will be meleeing far less. I stopped meleeing after the first few lvls of partying in the dunes, (around 12-14) simply because I wasn't doing damage with my weapon to speak of and it was distracting me from my primary role of enfeebler and backup healer.
Without getting too much into the roles of different jobs, RDM isn't quite a mixture of WHM and BLM. They have their own role to fill, based on what they are most proficient at, enfeebling and enhancing. Yes, the RDM can heal, and the RDM can nuke, but it does neither very well. They don't have the MP to replace a real healer, and they don't have the elemental skill to replace a real nuker. What they do have is the best skills for reducing an enemy's effectiveness in battle, and improving a party's effectiveness. The spells that RDM excells at will save valuable downtime because their enfeebles will reduce the MP output of the rest of the party, as well as the HP cost of the melees. A RDM can be the difference between making a EXP chain, or even between life and death. This is especially true in the dunes when you get to pugils. Everyone likes to see:
XRDMX casts paralyze.
Beach Pugil is paralyzed.
Beach Pugil readies Screwdriver.
Beach Pugil is paralyzed.
It is true that BLM and WHM get many of the same spells that RDM does, but they can't enfeeble as well. Their skill at enfeebling capps much lower than RDM. With gear in place to increase MND or INT according to the spell, you will be landing enfeebs on mobs that would take a WHM or BLM 3+ casts to land and wouldn't last nearly as long.
In the end, what matters is that you know the strenghs of your job, and play acordingly. Otherwise, you are gimping yourself. Will yu be an asset or a hindrance? The choice is before you.
I don't mean for this to sound like a lecture. This is a game, and it's supposed to be fun. And it is quite addictive. There is so much to do and see, it's easy to lose yourself in this amazingly in-depth world. Personally, I think RDM is the most exciting and versatile job in the game. It is also one of the two jobs with the potential for soloing, if you know what you're doing. Remember what is most important to spend your gil on, Spells>Armor>Food>Weapon. Some might not agree with me on this order, but from what I've played so far, that's how it works best for me.
Finally, learn how to make useful macros and use them. Macros are invaluable to saving time in battle. The best thing about them is the ability to temporarily swap gear quickly, according to the spell you are casting. This becomes more important later on, but you can begin right away. For instance, get a sword for melee and equip it as your main. Get a wand that has +INT and +MND and put it in your spell macros like this:
/equip Main Willow Wand
/wait 1
/ma Cure <stpc>
/wait 4
/equip Main Bee Spatha
This gives you a temporary boost to your MND for a stronger cure spell. It works well in early lvls before your cure is capped at 30 HP, and it automatically switches you back to your sword for melee.