B2P or Monthly sub? Also have they said what happens when scifi cancels the show after 1 season?
The season pass gives you free costume and other shit for the next year, b2p should give you most of the "game" content (free), they don't want a situation where some people can access some areas but others can't. There is also a cash shop for stuff, not much right now but expect many flavor items, vehicles, and tokens that help you get in game gear (not quite p2w but close).
There really aren't any classes in the game, your initial choices just are loadout packs and you can slowly unlock everything with ego points I think (super talent tree with everything in it, like AAs sort of). A lot of gear scales with your level so new stuff is more about mods (gems) and xtra abilities, or using it as salvage to improve your existing gear.
The game is buggy as fuck, and there really isn't any endgame, so almost everyone will be "done" within 1-4 weeks depending on how much they play. They hope to deliver rapid content patches to progress the story as the TV show unfolds, and Trion has had a good track record with Rift on patches, but who knows.
If the TV show wasn't launching next week I seriously doubt the MMO would be launching right now, and I think all the bug fixing is going to have them spinning their wheels for a while. They have also invested a crazy amount of money into this plus the TV show (over $150m), I have to wonder what their fallback plan is if the game doesn't meet some pretty high sales requirements. They need to sell over 1m copies to recoup dev costs for the game. On the good news side Guild Wars 2 sold over 3m copies so it is possible, especially with Defiance being PC+console.