I'll tackle staves first since they're easier to explain and Shirai already covered most of it
As mentioned Ice for Paralyze (and bind)- but also for the
huge elemental skill boost for us- which by far makes the Blizzard line RDMs most accurate nukes to use.
Earth, Wind are nearly as important- Slow is one of the
best enfeebles in our arsenal, Silence is incredibly important and Gravity does double duty with controlling mob movement and giving all the DD what amounts to basically a P.Charm for 21 MP. I'd say Wind is/should be a higher priority than Earth, but both are important.
Poison II is our best DoT spell, its cheapish and doesn't deal initial damage to the mob so no added TP there, and as an added bonus- doesn't overwrite Dia
Fire and Thunder- nukes, stun (at 75 with /drk), but also for the elemental enfeebles if you end up subbing /blm and have a reason to use Burn and Shock. Either way- you can wait on these for awhile, whether or not you get and use them will depend on if you actually plan on using RDM or retiring it after you reach 75.
I won't say having a full Elemental staves set is a must have for RDMs...but most RDMs end up picking up the entire set at some point.
Ok, easy part over with- now for rings.
MP- MP is good, MP lets us cast- but after its used up, that MP giving item is just so much wasted space. MP items used primarily for macroing in for Convert and the first heal(s)- and then swapped out for the real casting stuff. Can also be switched back in when your resting.
MND/INT- Fiye nailed it by saying RDMs are enfeeblers at heart and that several (not all) enfeebles are modified by one of these stats for added potency. INT and MND also have a small effect on accuracy for less resists.
MND- increases the amount Slow reduces Attack Speed, how many times Paralyze procs, how much HP Stoneskin absorbs, as well as its effect on Cure spells which I'm sure you're already familiar with.
INT- increases the amount of damage nukes do and the potency for Blind. Silence, Poison, Sleep and Gravity are all pretty much go/no-go spells. They either land or they don't and any accuracy boost they may get from INT hasn't been confirmed as far as I know.
I can provide links to some enfeebling tests/better explanations if you want them, but that's the basics.
Edit- Just realized I skipped over the AF tights in my earlier post. They're a coffer hunt in the ever annoying Garliage Citadel. Good steady piece for healing and enhancing skill- I still use mine for cures and SS but you'll want to macro in for MP and/or MND/INT.