I just bought this from PSN, anything I need to know before I begin?

There are two easy traps to fall into. First, upon hearing that leveling is technically counterproductive, you could become XP-phobic. Second, upon hearing that most ultimate weapons are available on the first disc, you'll set out to earn them. Both are a lot of work for very little benefit.

(For the first, leveling is basically a wash. Monsters do level up to match the active party, and they do get better boosts per level than your characters do, but they also give better "equipment" to even things out. It's possible to superpower yourself early in the game, in which case leveling is a straight benefit for the monsters. But you'll be grossly overpowered by then, so it doesn't matter.

For the second, upgrading your weapon basically upgrades your Strength stat by a few points. There are a couple of other benefits, but that's basically it. I'll cover what your real weapons and armor are in a moment.)

The first thing remember is to read the tutorials. FF VIII plays differently from most other RPGs out there. Assuming you can get by on levels and weapons will turn the whole thing into a painful slog. Don't do it.

Second, understand that junctions are your real equipment. Strength affects physical damage, Magic affects magical damage, Vitality is physical defense, while Spirit is magical defense. With the right abilities, you can equip magic to your stats. Stats drive just about every calculation out there. You want good magic, and you want to use it to raise your stats.

Third, experiment. The system is pointedly designed to reward a player who tries all sorts of different things. In the extreme, this can include unlimited copies of a full-party invulnerability item. Feel free to tinker around with everything available.

Finally, unless you're looking to figure this all out on your own, I suggest picking up a GF FAQ. GFs are not only fun, flashy attacks in and of themselves, they're what allow you to learn and use all the cool abilities in this game. Seriously, without a GF junctioned your characters can't even use items. You can complete the game with only a handful of mandatory ones, but it's more fun when you have them all.

(Third myth worth pointing out. People will tell you not to use GFs. There isn't actually any mechanical downside to using them. It's just that counting on them as your primary source of damage requires watching the same summon animations over and over and over. If your junctions are good, you can do comparable damage with other attacks in a small fraction of the time. Use summons when you feel like it. Use other attacks when you get bored. And know that a couple of late-game enemies punish summoning as a strategy, so do learn how to junction before that.)

If you run into a T-rex while you're outside with Quistis, she'll openly tell you that it's too strong and that you should run away. Proper junctions can turn it into a cakewalk, but it's still a really strong enemy for a beginner. It's not like you lose out on anything by running.

The time you select has no direct effect on anything. How much time you have left on the timer when you defeat Ifrit has a very minor and temporary effect, but it's honestly not worth thinking about on a first playthrough. You can look through the mechanics for a later playthrough, if you end up interested enough.