I wouldn’t add another entree. You have a red and a white option. By adding another entree you will be substantially increasing your cost and their cost. When you cater you have to have enough for everyone and the likelihood of everyone equally wanting the three is low.
I would add a couple of sides to make up for it. A very cheap option is green beans almondine. Literally green beans a bit of butter and some slivered almonds. Looks great on the plate and very cost effective.
You could also do a veggie tray…when we cater this is probably one of the most popular things we have. We get some really nice looking Kale (green and purple), broccoli, cherry tomato, cauliflower and baby carrots. Effortless to put together. We take our ranch dressing and add cheddar cheese to thicken it for a dip.
As for your salad we usually make it just before service and mix the dressing, assuming you will have kitchen facilities. If not make it last before heading out the door. If you have two bowls I would make one and while service is going I would make another that way it is crisp. Note of caution, use parm cheese not shredded and only put croutons on the top. Cherry tomato is a better option than sliced.
Hope this helped.
Kris