This question is a week old so I might be too late to help.
I've been catering for 15 years. So this is just my personal experience.
I understand what the client means by running out of food. That is not a problem or going to make you look bad. They do not want leftovers, do not want to feel cheated if you take a bunch of food back with you and want to control costs. If you make at least 150 good sized servings and it goes, then it's gone. You snooze, you loose. Just make sure there is enough for everyone to go through the buffet line once. And make it so you can refill items instead of having everything laid out at once. This will deter people from taking a lot, because this will be before dinner when people are hungry. As you mentioned it's not a dinner, it's a gesture of the host.
The nuts will be fine. These comments saying about people eating with their hands in the bowl? Yeah that's gross, but it shouldn't even be an option for them. You will need a plate of some kind for all of your foods. I recommend a 6"-7" hor D'oeuvre plate (disposable plastic) for all the dips, nuts and fruit to go on. Check out a local supplier or online. That way it will fill up with less product. Make sure to have at least 200 small plates for the people who come through again.
Quantities. Depends on what the client wants to spend. Especially with the almonds, as they will be the most expensive. So put them at the end of the line. The almonds would be best served with a 1 ounce serving spoon to control cost. Serving spoon sizes greatly impact portion control. Most people take 2-3 scoops of an item automatically. I'd go with 7 lbs. of almonds. Cut the grapes stems into sections of 5-8 grapes so they are easy to pick up (with tongs). Depending on size you can get 8-10 servings per bunch of grapes. The dips since there are 3, I would go with 3 quarts each (2 1/4 gallons total of all 3) and about 10 loaves of different kinds of cubed bread and 10 boxes of different crackers.
Make sure every item has tongs, forks or spoons (including bread and crackers).
Have plenty of small plates and cocktail napkins.
Wet naps are a nice touch with finger foods, so people can wash their hands.
As I said, just my experience. Hope I could give you a good idea.
Most of all have fun.