Bethesda's Todd Howard dropped some details about Fallout 4 during the open-world game's presentation at Quakecon. There'll be about a dozen companions in the game in addition to Dogmeat, and a couple were revealed during the presentation. One of them was Preston Garvey, the faction leader of The Commonwealth of Minutemen. The other was a woman named Piper who comes from Diamond City, which used to be Boston's Fenway Park.
If players wish to journey across the wasteland alone they can do so, and instead of being punished for it they'll get special perks instead. If they do travel with a companion however, they can choose to romance them regardless of gender. I don't think that applies to Dogmeat though. It was also revealed that there'll be 70 perks in the game, and each has its own rank which amounts to 275 ranks. They're tied to S.P.E.C.I.A.L. stats, and players will receive one perk per level up regardless of whether they have companions or not.