You're in NYC, it's winter. So, profile your client (& guests). Always good to have enough for vegheads to eat.
Depends on equipment, type of service (drop off, full service, plated, buffet,...
where are you?
I've loaned out my kitchen to a visiting pastry chef who wanted to make his niece's wedding cake.
Your friend should be able to prep & cryovac ahead as well as plan a menu that needs little kitchen time.....and...
Service fess in offsite catering are standard practice....18-20% covers shtuff
delivery charges are either added into the cost of doing business or a nominal fee
Tips in my mind are just that....optional.
It'd be good if...
mashed potatoes or jasmine rice or potatoes au gratin with guyere
green salad with lots of goodies on it.....ie craisins, pecans, hearts of palm, sugar snaps.....vinaigrette