1. During the new character creation process you are guided all the way down to choosing an estate for your character. If you follow the process the whole way, you start with an estate.
2. Nobles without an estate can assign themselves to an army. This was not really the intended, ideal way for it to happen. It's a workaround. The original intent of this feature was to have a way to get those upper-level nobles without an estate (rulers, dukes, lords, etc.) a way to get into an army. It was applied to lower-level nobles to both ease implementation and to increase playability for characters without lords..
3. If your family is famous enough, then your characters start with enough H/P to be assigned to lordship, and perhaps even a ducal title, from day one. Aside from that, yes, it can take quite a bit of time for a new character on a new account to accumulate enough H/P to be able to get a lordship. This is highly realm-dependent. Some realms have lots of opportunities
Overall, though, you're correct in that delivering this information to new players is critical. It's hard to present in a timely manner before/during account creation without blasting a new player with a wall of text that many (most?) won't read. Then when they're done and have already created the character, those pages are no longer accessible. Quite a few players have used the wiki to document this stuff before. But it's hard to keep it updated with various game changes.