Really depends on what you are going to do.
You need some really good runic crafted arms and legs for resists the rest (lrc/lmc/fc/fcr) is pretty simple, and you'll have some MR as well. A very basic easy to get started suit that wont cost you too much money:
Helm - Kasa of the Raja (80+ resists)
Neck - Pendant of Magi (30 LRC, 3MR, LMC 10, SDI 5, Intel +10)
Gloves - if you are elf - Stitchers Mittens (30LRC and 51 resists)
Chest - Rune beetle carapace (there are other options here, but RBC provides 3MR, +10 mana and 15 LMC.....lacks resists only like 38 total......heart of lion has decent resists and also provides DCI.....or better when you can afford it, a well player made tunic)
Tali - Totem of Void (10 LMC)
Arms/Legs - Need to be barbed runic kit made and high in fire and poison, energy and have some LRC......these can get costly, but those are the areas you need to focus.
For the casting portion - Chaos Vesper Shield provides 1/2 casting buffs and a basic scrappers compendium gives 1/1 plus 10 LMC and 25 SDI....so you are at 2/3 and now only need a 0/3 ring OR braclet to max out magery casting (1/2 and a 1/1 for max chiv casting). One of them needs a little bit of LRC.
With that very basic suit you'll be 100 LRC, 40LMC, 6MR (perhaps more depending on crafted gear), 42 SDI and probably 50+ in resists so long as you get a decent set of arms/legs, and thats without really factoring any additional bene's from your ring/braclet.....as you progress you can make/buy better arms/legs and begin to more properly tailor your suit to your play style (moving away from the PoM and RBC to high end crafted gear, scrappers w/ additional mods etc).