Did you end up getting them? I would love to see pics. I agree with the others, the more the merrier, but at least you are planning to get two. I have had to separate out one in a quarantine tank, and they get what I call "lonely discus syndrome."
The biggest risk of plecos sucking on your discus is if they aren't feeling good and are down towards the bottom. (no duh right...) Most of the time a happy discus will be in the mid to upper water column at the glass begging you for food unless they are picking food off the bottom. So I would just keep a watchful eye on them for the first few days and watch for marks on the side. When you first put them in they will very likely head for the bottom for a few hours.
Also, if you haven't purchased them yet, make sure they eat very well at the store. A discus that doesn't go after food is sick. Luckily the bigger ones tend to be hardier. Also, once you have discus you will want to make sure to quarantine any new fish you add (just in case you dont already). You may already know this stuff, but in case you didn't I thought I would mention it. Have fun, those sound like great fish for a great price.