"On music programming, you may already know that a lot of DJs use the 'old people' music first, then work their way up to more modern material. My opinion, it's a waste of time and you lose guests because of it..
As you noted, "if this works for you"...then go for it.
Personally, I use the "play the oldies first" as a selling point.
If I am pitching to the adults, they are RELIEVED to hear that I won't forget about the grandparents.
The bride and groom and glad to know that I intend on making sure the "old folks" tire out early,
so they can end the night hearing what THEY want to hear.
Funny thing is, it's kind of related to your "four song" plan.
I usually go in blocks of four or so, changing tempo, genre, and age.
I just concentrate of the older guests in the beginning....as long as it fills the floor.
If not, on to PLAN "B".