So, I’m trying to get the golden ending for Alice and I’m currently at over 220 affection points and I just unlocked the feeder scene. Is there anything more I need to get the ending or do I play it straight from here?

Unlocking the feeder scene is not one of the prerequisites. You will need to have played all the optional scenes, and you can't have made more than 1 bad decision that contributes to getting the bad ending. 

That includes all of these scenes: WGGTS001, WGGTS002, WGGTS003, WGGTS004, WGGTS005,  WGBE001, WGBE002,  WGBE003,  WGBE004A,  WGBE004B, WGBE005, WGAE001, WGFMG001, WGFMG002,  WGFMG003,  WGFMG004A, WGFMG004B, WGFMG005, FMGWG001, WG001M, WG002M, WG003M, WG004M, WG005M, WG009, WG011, WG013, WG014, WG017, WG018, WG021, WG023, WG032, WG058,  WG065,  WG083. This list may get longer as more optional scenes get added to the route. 

The route guide explains how to get the bad ending so you would just not want to make those decisions on the route.  https://www.deviantart.com/the-murp/art/Alice-Route-Guide-Growth-Academy-1236746..

So, after I complete all the optional scenes to get the good ending, are there any specific changes that happen throughout the rest of the route that let me know I'm on the right path?

There are some dialog forks that indicate the bad ending is active but there are only a few of them, but they don't necessarily tell you that you'll get the good ending since the optional scenes required to unlock the best ending are throughout the route all the way up to almost the end of it. 

Okay so, can someone spoil the golden ending for me? What exactly happens?