People are okay with a base level cap of X, to be raised to X +10 or 2X or whatever in a future Epic supplement.
Yes, though I think level 3 is still too low in 3e (because you level-up so fast). The first 6 levels would work well mechanically, and get you fireball and fly, plus all the basic monsters up to a few iconic "level 7" ones (CR 5, the Manticore, Troll, and Wraith). That's the D&D most people seem to play.
Maybe just 6 classes, Fighter, Rogue, Adept, Wizard, Cleric, and Bard/Druid.
Where Adept is the martial adept and gish type, a barbarian/monk/psiwar/shifter deal.
[*]A 2nd pair the same sizes would net you the rest of the core game, level 7-16 might be a better stopping point than 7-20, and adding typical prestige path/class options could fill out your page count. Could have PClass rangers and paladins and alt-wizards and spec-clerics and ..., splatbook filler forever. Cold Guy, and Frostmancer, and ice-knife.
[*]Churn out a 3rd pair for rulership and background income, mass combat, trade, boats, flying ships, city-building, and all the bullshit that wouldn't fit earlier, levels 1-16. Include all the noble, criminal, and monstrous secret-overlord societies like Illithid elder brains and drow plots against the overworld. Totally add a courtly social mini-game if anyone can write one that isn't a bag of ass.
[*]A 4th set for planar adventuring and world-rending catastrophies, a few "I'm a god now" epic classes for 17-22 (6 of them, for the original six classes). Get into vampire plagues and nanoswarm cascades and other things DMs may or may not want to bring to the prime but can totally work anywhere as a planar jaunt. The blood war, the fury of angels, the great walk, a dragonflight. Plus all the 9th level spells you ever wanted.
You know, what they tried to do with 4e, a money-making scheme, only something people might totally buy once they're bored with the last lot, not just more of the same. Pathfinder2, eh. Monsters and treasure and encounter generation in the DMG, everything else in the PHB. Not monster books, but monsters and interesting things you can do with them. /rant.
PC, SJW, anti-fascist, not being a dick, or working on it, he/him.