Is it possible to progress or play "end-game" without being a credit card warrior? Does one require a subscription like in SWToR to access everything in game, including end-game?

You can technically do anything in the game (except almost all of PvP) without paying a dime. Whether it's viable or not depends completely on how insane you are.

yes, its pretty easy. You are rewarded "TP" Turbine Points for playing the game and accomplishing deeds.
Examples, kill 100, 200, or 300 creature types in an area. Find certain locations. Complete puzzles or riddles.
When you complete a deed, youre character is awarded +1 to a specific predetermined trait, which is helpful and necessary.
So for building up youre toon, you are rewarded and you can use the TP rewards to unlock certain content. Alot of fun and addictive.
Id suggest going as a LM and you can have a beefy pet kill mobs while you afk and work on easy deeds.