Grand Theft Auto Online – Can Penthouse Owners Replay Casino Missions as Hosts?

As far as I know, performance is not a factor. I believe you received 50% of the normal payout because you completed the mission already.

Once you have completed a mission, you only receive 50% of the cash reward for subsequent completions. I believe this only occurs when the party votes to replay the last mission during the voting screen.

So, the other 2 players probably were not present for your previous plays on that mission and therefore got all $9000.

As turbo pointed out, you will also receive half payout if you do not meet the required level of the mission.

To play on custom maps, other players currently have to go through the Rockstar Social Club website.

From here they will be able to find your game and bookmark it which will cause it to show up in game so they can get back to it quickly in the future using the beacons on the map (bookmarks are gold).

Alternatively, as you've mentioned, you can host a job through the online screen (Online>Jobs>Host Job...) and then invite your friends/lobby members/whatever, just like you would in a normal lobby. This way they don't need to bookmark the job beforehand, it'll be automatically loaded for them when they join.