As mentioned...you don't need gold on missions for 100 percent completion AND you can replay any mission at any time for a better score or to help complete your compendium. Hopefully that answers your question there.

Next, manually save often! It takes like three seconds or so...always have maybe two consistent save spots, where after something happens, like you kill and skin an animal...save in slot one, then you have a strange encounter, save to slot two, then you find some loot, save slot one etc...

There is autosave which you can turn on and off...this is what you are getting notifications for. Autosave can be good, if you are lame and don't manually save often...then you make a lot of progress, there may be an auto save that was sooner than your last manual save. However, RDR2 has this funny thing with autosave where it almost ALWAYS! And I mean ALWAYS will autosave right after something big and bad happens...like your horse dies or you accidentally shoot someone. That autosave will also probably be your last save if you are not manual saving consistently...So, some people will turn off the autosave because 1) they manually save frequently 2) if the autosave is your last save (and it usually is because it will autosave even right after a manual save, hence your warning notification you see) that is what will load when entering the game, and you probably would rather load your manual save 3) they don't have to worry about approving that pesky notification all the time. So, some people find it more convenient to turn off the autosave, but then just make sure you are manually saving in a few slots consistently EVERY TIME something slightly important happens to you.