Please expand your question. Fire Emblem: The Sacred Stones or Fire Emblem: Rekka No Ken? If you mean TSS, do you mean Erika's mode or Ephraim's? It does depend on which game you are talking about, some Fire Emblem games don't even have parts.
you kill the evil hillery Clinton in the second door to the left
Eliwood automatically joins your part in Fire Emblem and no recruitment is required.
You get him in part 4 final-1 automatically
Part 4 Chapter 3.
Yes. He becomes a vanguard at the end of Part 3.
You will automatically receive him on your second playthrough of the game in Part IV. If you don't kill him in Part 3
On your second playthrough, when you have to decide how to kill him in Part 3, you can choose to spare him. Then, in Part 4, he joins you in one of the chapters.
It really depends on which fire emblem your talking about. If you want the main character, they're usually the ones of the 'Lord' class. For example, In the first Fire Emblem game and its sequel, Marth is the main character. There is also a large cast involved in every Fire Emblem game. The first Fire Emblem to be released outside of Japan (Fire Emblem 7: Blazing Swords) had three lords; Lyn, Hector and Eliwood (the latter being the father of Roy, the protagonist of the game's sequel, which was never localised.) In Fire Emblem 8: Sacred Stones, the lords are Eirika and Ephraim. In 9 and 10: Path of Radiance and Radiant Dawn, respectively, Ike is the protagonist despite not starting out or finishing as a lord, and Micaiah is also an important part of the latter game. Other than the lords, I previously mentioned there being a rather large cast of playable characters in each and every game.
Part 4, Chapter 3, Distortions. Baselard is at 12E and 10N.
No, Roy is not manakete. If Roy's mother was Ninian, a dragon, he would be part dragon, but still not a manakete
You meet him at the end of Part 2, after Elincia's Gambit, in a cut scene
How did you get him killed? In the tower, you have to kill him to advance. It's part of the storyline