For the fun of it since this was relevant to Snow/Nina in the CK DL and it isn't listed in this topic... the FF13 stat topic already lists what the cast can resist:
Resist Debrave | Giant's Glove, Warlord's Glove
Resist Defaith | Glass Buckle, Tekite Buckle
Resist Deprotect| Metal Armband, Ceramic Armband
Resist Deshell | Serenity Sachet, Safeguard Sachet
Resist Slow | Glass Orb, Dragonfly Orb
Resist Poison | Star Pendant, Starfall Pendant
Resist Imperil | Pearl Necklace, Gemstone Necklace
Resist Curse | Warding Talisman, Hexbane Talisman
Resist Pain | Pain Dampener, Pain Deflector
Resist Fog | White Cape, Effulgent Cape
Resist Daze | Rainbow Anklet, Moonbow Anklet
Resist Death | Cherub's Crown, Seraph's Crown
Debrave is -STR, Defaith is -MAG, Deprotect is -PDEF, Deshell is -MDEF, Slow is the usual, Poison is the usual (FF13 poison is not very scary, FWIW), Imperil reduces elemental resistance by one level (usually equal to double damage - neutral becomes double, halved becomes neutral), Curse is "you are easier to stun-lock and make you lose actions from being attacked", Pain is "physical silence = no physical-based abilities, including the base Attack", Fog is Silence (no magic-based abilities), Daze is [Stun/Stop/Sleep], Death is Death.
You can stack the same equip multiple times. The effect is multiplicative. Putting three 30% accessories on is 1-0.7*0.7*0.7 = 65% resistance. Three 45% accessories would be 83% resistance to the status ailment. Three 60% accessories is 93% resistance.
As for the stat penalty, if any... it depends on whether you use base unupgraded lvl. 1 accessories bought from the store, max-upgraded lvl. 1 accessories, lvl. 2 accessories, or maxed lvl. 2 accessories. The more allowed, the better the status blocking, but the larger the stat penalty.
For sanity's sake, just looking at lvl. 1 unupgraded storebought competition:
Platinum Bangle HP: +400
Warrior's Wristband Strength: +100
Sorcerer's Mark Magic: +100
General's Belt Resist Physical: +15
Witch's Bracelet Resist Magic: +15
Royal Armlet Resist Damage: +5
Entite Ring Elemental Resistance +10
Whistlewind Scarf Tiny ATB boost on turn 1
...and some other odd things like Lightning Affinity + Critical Barthunder, which I'll ignore.
Anyway, weird things happen in the DL if you let characters equip how they like for each fight with things like Witch's Bracelet / General's Belt depending on whether they're fighting a mage or not that tend to result in either screwing the cast vs. "balanced" opponents by holding them against an average that assumes they stacked the "right" resistance, or letting the cast screw over one-note opponents. So if you want to assume 3x of the "best" yet most general accessory, that's probably 3x Royal Armlets, and the cast arguably is extra good against elementally-reliant opponents by swapping that to 3x Entite Rings when fighting Fire Emblem mages and the like. If a dueler swaps in a status blocker, they take ~5% more damage for each one, or 15% damage for 65% resistance in the case where there's just 1 status the dueler cares about.
If upgraded lvl. 1 accessories are used, Royal Armlet upgrades quite nicely to ~15% damage reduction per, but the status blockers go from 30% reduction per to 45% reduction per, or 83% combined if just 1 status is cared about being stopped.
If you're me, the penalty isn't nearly as harsh since even though the storebought attack-boosters are kind of scrubby, I'd factor 'em in along with the other options. To make the numbers add up to 10, I will arbitrarily assume that FF13 characters get a magical combination accessory that is a basket of 3 Royal Armlets + 1 of each of the others listed above in each slot, averaged out. This means -40 HP, -10 Str, -10 Mag, -1% Elemental Resist, -2% first turn speed, -2.5% Physical resist, -2.5% magical resist for each status blocking accessory equipped.