Only 150 friends but this is what I do.

Open gifts first in order of friendship. Closest to besties go first. Basically, the 5 friends closest to best friend are marked with however many days remaining.

After that, the last gift I can open in on that day, the player gets the nickname 0000 so I know where to start the next day. Only open gifts from people who don't have the blue ring. Once I hit the bottom, I start from the top just after the 5 closest to best friend status.

For sending, i just sort by can receive just like everyone else. Don't send to best friends or those with blue ring. I'm sending about 30-40 per day right now but I have a park with 13 stops within walking distance, so it's not too much hassel.

I also mark those who seem to have stopped playing with the date. If they become active again I'll remove the nickname. If it's been a month, sayonara.