You want to level up your Q 1st no matter what. Anyone who is telling you to lvl up a different ability before Q is giving you bad information.
You only need to take 1 point in your ultimate on Pantheon.
Try using revive/ignite or revive/exhaust always.
Fight in short bursts. Spear throw, jump/stun, heartseaker, spear throw. (Q,W,E.Q) This should do alot of damage and you shouldnt have to stand in melee using many auto attacks at all. Harass with your Q a couple of times to get your opponent low enough to finish them with your combo.
Pantheon is best played as an assassin which can be tricky on crystal scar. Just move in and out of fights quickly instead of trying to go toe to toe with bruisers and such.
You should always build an item with CDR and almost always build an item with some armor. Maw of Malmordius is a great item on Pantheon.
ghostblade, phage, maw, atmas are all exceptional items.

This is a fairly heavily debated point. I myself split level Q and E.

While I don't discount the advantages of Revive on Pan. I don't think it's mandatory. Both Exhaust and Ignite are extremely good on him and taking both of them and leaving out Revive is viable.

I agree, harass with Q. But once you jump in, most of the time you have at that point relinquished your ability to "fight in short bursts". Unless they just decide to ignore you, you have no way of disengaging. Generally your CDR is high enough that you don't AA much because you have an ability to use every 2-3 seconds. And Pan's passive, plus W actually enables him to be quite survivable in a drawn out fight. As well as his damage is so high that he can build a coupe of tank items(as you recommend below) and still do significant damage. I'm not saying that Pan should try to tank in a team fight. But he is quite durable and deals such high damage, that committing to a fight is rarely a problem for him.