|Pathfinder Adventure Path, Campaign Setting, Companion, Roleplaying Game Subscriber||
Don't try to be epic - epic comes from having an engaged player group who in turn make things epic...if that's why they're gaming. It's hard to explain but if your players want to have a low-level dungeon crawl there's not alot of room for epicness. If, on the other hand, they want to have a bildungsroman or monomyth-esque adventure then epic is what they're aiming for.
Have an outline, not a script. Months of planning and storywriting in your head will be dashed by a single player's actions. Make an adventure flow-chart if your going for epic and highlight the "required" scenes. The connectors that go between the scenes are where you have to be fluid because that's where the players have the most control and where you as a GM have to give the perception of choice or else the verisimilitude will be lowered.
The thing about old-school gaming is that no DM ran the game exactly the same. PF codifies things (actually the OGL did which is why, IMO, the d20 craze worked very well - every "old school" homerule could now be bound into the layers of the OGL and published) and is easily accessible via downloadable system reference docs (SRDs). 1st and 2e games had TSR material, Dragon Magazine, White Dwarf, some 3rd party publishers (Arduin, Judges Guild, other heartbreakers - my fave was Bard Games Arcanum) and fanzines for it's content. Due to the lack of material you were forced to make up alot of rules, content and this resulted in your own personalized brand of D&D that was only known by the amount of players you gamed with. With my cooking background old-school D&D was like chili...yes...chili. Most folks used the basics; meat, some tomato product, onions, garlic, and beans (for us northeners:)) but travel a few miles and then you find somebody who added broken spaghetti (ala Real Chili right here in Milwaukee) or someone who added cinnamon, or someone who did not use beans, etc. It was all "chili" but based upon the taste of the creator and his or her influences. In D&D this equated to all folks using a d20 to hit but some allowed no racial/level limits, some used Method V for rolling characters, some used Wolfgang Baur's Paths of Magic article from Dragon...all was D&D but each DM or gaming group adopted their own variations.
While this level of modification is allowable in today's PF world the intertwined aspect of the OGL makes adding or subtracting things more complex in that you have to do some litmus tests on your modifications, i.e. by removing a rule or option what downstream impacts may it bring forward. It mostly affects using pre-written material that does not follow your tweaks and thus increases prep time to modify the material to fit your variants.
I apologize for the stream of consciousness post but it's early and I haven't had my coffee yet.
Natural Twenty Games
(gaming since 1979 or thereabouts)