I suspect you may eat even more eggs when you have your own hens. The fresh eggs are delicious.
I have no experience with either Plymouth Rocks or Buff Oringtons, but I've been reading and reading for three years and I can easily summarize the generalities I have come across regarding both breeds, because I've been looking at them, too, in the bantam size. Barred Rocks are one of the top favorite breeds for backyard chickens for both laying and friendliness. People love their Barred Rocks. I don't know if they are friendlier than the other Plymouth Rocks, but the Rocks in general are said to be smart, curious, friendly, independent, neither bullies nor bullied by other breeds, and of course, the Barred Rocks can be sexed at hatching, which I suspect has helped their greater popularity. However, the roosters are usually more aggressive than the hens.
The Buff Orpingtons are the #1 most popular breed for being sweet, friendly, and good layers. They and the Plymouth Rocks lay about the same number of eggs on average. People adore their Orpingtons. Many people say their BO roos are also quite nice compared to other roosters. The BO is a slightly larger bird than the Rocks. I would read the breed reviews on this site and see what others say about both breeds.
For myself, I don't eat meat, so I don't need or want "dual purpose" chickens. Are you or hubby going to slaughter the cockerels you hatch out and don't want beyond about five months old, or do you plan on selling the babies locally? You have a big family? You may want to raise your own table birds.
I'm not sure what the big deal is with one breed or two, apart from the fact that Orpingtons are often picked on by other breeds. If you want to try two different breeds together, the easiest time to get them both is at the start when they first hatch. Personally, that's a little too controlling for my taste, and as an old, long-time single woman who built her own coop and will do whatever I please with three-dollar chickens, I say get what you want and see for yourself which breed you like best, or if you like them both. You can sell any you don't want locally. And if hubby (who won't help to begin with) makes anything of it, put an ad out for him, too. You can see why I have been single almost all of my life.
Personally, I recommend doing what you want . . .