You got it right. Warm-up like normal and then fire off 5 reps for one set, anymore would probably be counter-productive. It's what I've been doing with good results and no burn out.
As for your plan, it would all depend on your goals and the potency of the metcons. I'd say dropping the Wednesday session in favor of rest a rest day could produce some good strength while keeping up your conditioning.
I'm not the most experienced or knowledgeable in that regard but I kind of like the idea and might try it down the road when I try to get my lungs back and lose my ass.
Healthy body sick mind...