Sealed Temple Strategy

Magic
These are the bare minimum magic spells I would have before entering the Sealed Temple, as many have limited or no use. However, you'll probably buy all white, black and time magic throughout the course of the game anyway, so those sections are probably not relevant to most people.

White Magic

 * Libra
 * Poisona
 * Mini
 * Cura
 * Esuna
 * Curaga
 * Arise
 * Holy
 * Dispel
 * Raise/Arise (Just in Case of K.O.)

Black Magic

 * Toad
 * Bio
 * Firaga
 * Blizzaga
 * Thundaga
 * Flare

Time Magic

 * White Wind
 * Mighty Guard
 * Magic Hammer
 * Level 3 Flare
 * You may want Dark Spark and the other level-based spells, but I rarely use them.

Summon Magic

 * Golem
 * Carbuncle
 * Syldra
 * Odin
 * Leviathan
 * Bahamut

Useful Command Abilities

 * White Magic 6
 * Black Magic 6
 * Time Magic 6
 * Summon Magic 5
 * Blue Magic
 * Dualcast
 * Mix
 * Spellblade
 * Rapid Fire
 * Jump
 * Zeninage
 * Sing
 * Catch

Useful Passive Abilities

 * Dual-Wield
 * Counter
 * Find Passages
 * Light Step
 * Shirahadori
 * Sprint
 * Vigilance
 * Learning (if you still need Blue Magic)

If you use a setup of Freelancers and Mimes, you can get all of these abilities and more without having to equip them. This works fairly well for most random encounters and boss battles. You could switch around the four magic types on the Mimes, but I like to keep Blue separate. I also tend to keep Time and Summon apart, in case there are situations where I would like to call Golem and Carbuncle as well as Hastega (And Blue for Mighty Guard, obviously). When using this setup I give Bartz the Hermes Sandals and Brave Blade/Chicken Knife, so I can Rapid Fire vs. random encounters and set up Mighty Guard vs. bosses.
 * Bartz: Freelancer - Blue, Rapid Fire
 * Lenna: Mime - Dualcast, White, Summon
 * Krile: Mime - Dualcast, Black, Time
 * Faris: Freelancer - Spellblade, Rapid Fire

Equipment
Bartz Lenna Krile Faris A lot of this equipment will also be replaced by equipment found in the Sealed Temple; in my setup, Lenna gets the Force Shield, Krile the Vishnu Vest, and Faris the Grand Helm and Maximillian.
 * Genji equipment
 * 4x Hermes Sandals
 * 4x Flame Ring
 * 4x Coral Ring
 * 4x Angel Ring
 * 3 or 4x Elven Mantle
 * 1 or 2x Aegis Shield
 * 2x Gold Hairpin
 * Brave Blade/Chicken Knife
 * Ragnarok
 * Excalibur
 * Magus Rod
 * Sage's Staff
 * Air Knife
 * 2x Crystal Armour
 * Crystal Helm
 * 4x Ribbon
 * Brave Blade/Chicken Knife
 * Genji Shield
 * Genji Helm
 * Genji Armour
 * Hermes Sandals
 * Air Knife/Sage's Staff
 * Aegis Shield
 * Gold Hairpin
 * Crystal Armour
 * Elven Mantle
 * Magus Rod
 * Aegis Shield
 * Gold Hairpin
 * Crystal Armour
 * Elven Mantle
 * Ragnarok
 * Crystal Shield/Excalibur
 * Crystal Helm
 * Crystal Armour
 * Elven Mantle

Stats
I am normally around Level 40-45 when beginning the Sealed Temple, with around 1500-2000HP.

In terms of job mastery, I would normally have everyone master Monk, Samurai and Mime (Monk for Counter, Samurai for Shirahadori and Mime for Mimic) and then have others master the jobs necessary for their ability setups (e.g, Bartz and Faris would master Ninja for dual-wield, as well as Ranger for Rapid Fire, etc). You can master other jobs to get their inherent stat boosts but I don't usually find it necessary. Of note, I would have Lenna and/or Krile also master Chemist for the Mix ability, which is situationally useful, and I also have everyone master Geomancer and Bard, simply because it only takes one Mover encounter to master either of those two jobs.

As I complete the Sealed Temple with Freelancers and Mimes, I never gain any ABP while inside, but by the time I'm finished with everything (including superbosses and Cloister of the Dead) I am usually around Level 50-55 with 3000-4000HP.

Items
Before entering the Sealed Temple, I always buy 99 Potions, Hi-Potions, Antidotes, Eye Drops, Gold Needles, Maiden's Kisses, Mallets, Holy Waters, Phoenix Downs, Tents and Cottages. I also usually get around 50 Ethers and 40 Elixirs (you can get more if you don't intend to use Zeninage at all). If you intend to Drink at all, you could by 99 of all of those items, but I never do.