Main Leaderboards are updated between 1-2 hours.
Names listed on the leaderboard are what they were at the time a score first showed up on the leaderboard. Names will occasionally update over time if a player continues to get new or better leaderboard scores.
At this time it's not possible to. Each main leaderboard will only show the top 20 for each platform while the onslaught, prestige, and mastery shows the top 100.
These are actual player names since its possible to have a blank name on Steam.
The solo leaderboard requires that you were solo the entire time. Even if a friend was in your game for 1 second or left before you started the match, the game is considered a team game at that point.
Not at this time.