What would you describe "we" as? Amount of food is going to be different for senior citizens (who may need to watch sodium intake and avoid high-sodium food like snack mixes) than a hungry bunch of teens who seeming are human vacuum cleaners when it comes to food, or something in between.

You can Google - party food calculator - that might help you out with amounts of food to serve.

I would look at the back of the package in the nutrition box and use the servings-per-bag as a guideline, but since it will be served along with other food options, I would figure 1-2 servings of "mix" per person.

-Grainlady

I think a cup per person is a good amount, then i double it. I don't mind leftovers. I usually make three while i'm at it and make ones we like.
A spicy-salty, an Asian ginger coconut toasted chick pea w/wasabi, a dark chocolate using my granola and add puffed rice...not very kid friendly but i like to make Pocky for them if i expect some kids. I did make the popcorn rice ball thing once but too sweet for us.
I don't put it all out at once but have it handy to re-fill. Just behind the bowls on the sideboard. If someone really like one, i'll pack up a little go-bag and offer the recipe.

It's a good idea to have a salty snack, veggies and dips, and the sweets/cake. Your menu seems perfect.
Something for everyone. And everything can be made ahead of time.
I'm terrible at dessert things but have made a decent brownie and recently made ice-cream sandwiches.

-the party mixes do freeze well if you make too much. Portioned in small bags, then all in a big gallon zip-lock for a grab-n-go. (i had 'small zip-locks' on a grocery list that means qrt freezer bags but DH bought the smallest thing i've ever seen...and as thin as saran...but works for a few nuts and mix)

Not sure where you live, but being in NY half of my guests are from all over and english is their second language....so i print out the ingredients/recipe just in case someone asks. Especially for dips and dressings.

Thanks!

It's a casual wedding reception for 120 to 150 people, starting at 2 or 3 o'clock. Not a sit-down affair. So people will be mingling and talking. Food served on small plates, and possibly with nut cups for the snack mixes.

Would you revise amount, based on that?

Yes, I want everything made ahead of time, and not needing to be served hot or super cold is the criteria, to keep things simple!

Can you share your recipe for the Asian ginger coconut mix?

Oh my, i was thinking a few dozen in and out of the home and garden. : )
I've hosted a couple weddings for friends on my farm and did simple, as you are thinking...
One was October but unseasonably warm, Hot!. I stuck with the veggie plan but had to put ice in baggies under the platters and dip stuff. (the meal and party moved on to an event place later).
I hid the ice under fabric. I also was making spring rolls for every event at the time and that took way too much time the morning of. But great for the wedding party 'girls' prepping in the second floor of the barn. Healthy and fresh and the brides favorite so i made them for her and the rest went out on the table.

I'm terrible with recipes because i want to fuss and take a bit from this and that and take out the sugars...
And use what i have that is available without too much shopping. If i needed to make one today?...in the freezer i have pecans, dates, a big bag of raw shredded coconut and a big hunk of ginger in the fridge. And a bag of chick peas...and some wasabi in powder form. I made candied ginger last month and it was amazing but can be bought. So using a few recipe ideas, some can be combined. Like this list, i'll give the link...
I have some puffed rice cereal from the health food store. Some pepitas, (hulless pumpkin seed), and if i toast the coconut, whizz some of it to coat the chopped dates...toss with roasted chick peas, (not the sweet recipe but the savory one) ...toss what seems good and back in the oven on low 200 heat for an hour...
You may just invent your own mix by tasting and adding a bit more spice, etc.
(a bit of warmed coconut oil, just a couple tbsp, is amazing flavor that helps give good toasted flavor and give some binder glue for any powdered spices).

Of course make a mix you are comfortable with that is not a stressful new one, but my crowd likes my 'adventures', lol.

-and, yeah, my amount per person is way high for a big event. And probably not much help with the mixes...but if you have time to experiment and have fun in the process...big win in the appreciation game. -if any oils or butters are in your mix, you have 4-5 days in fridge, any longer do freeze for freshness...

Here is a link that might be useful: snack mixes

I didn't know you could freeze snack mixes. Can you freeze ones with crackers/pretzels? Only nuts and spices? Chex mix? I had no idea.

Did not know that chex was putting a party recipe mix on the box as early as '52.
A Betty Crocker book had a Kix party mix in 1950. I thought it all started with some of the early 60's magazines and all the experimental 'snack' creations that are so funny to look back on...

I used to think of an auxiliary freezer as a big wasted energy hog. But it keeps bulk nuts, seeds, spices, breads, crackers, and stock, summer produce, fresh.

Some party mixes, especially the earlier recipes use butter and oils that can go rancid. My mother always started the holiday season at Thanksgiving with big batches of party mix and would freeze it...mostly to hide it from us, (but we always found it.) My earliest memories of cooking experiments were trying different combinations of cereals and spice, Old Bay, etc.

I make bulk granola just three times aprox a year and freeze. It has lots of seeds and nuts and best if frozen for freshness. I use coconut oil that is very stable but the grains and oats etc are much better kept frozen. Even a bag of chowder crackers that are nothing special, a childhood memory, but regional and hard to buy..i freeze.

Some mixes that have been in the freezer for a few months can be re-freshed in a low oven for 20min. I've done that with granola when i pull a batch out...I have one left from september that i want to add some dates and some pepitas so i'll re-toast it.