Then, I suggest two griddle plates and one burner.
Most of the time, for just the two of you, you'll probably end up using one of each of the grills and griddle. The latter is perfect for stir-frying or sauteeing veggies while the meat is cooking, or used as a warming plate to keep stuff hot while you're still grilling.
We're going to get the cover for ours and a full-sized tank to keep it set-up all the time on our patio for convenience. But, if space is an issue, it sets up in about 5 minutes.