How much mulch ?????

3" enough. 10 will kill weeds and everything else. 75 sf will do it. (a full size truck bed). You have to get it from a mulching co. not bags, and i recommend install weed fabric under the mulch. If you don´t have a truck, they deliverer to you.

I mulch to keep the soil cool and protect my drip lines. I live in Southern Arizona. I wouldn't use 10" of mulch. Why so much? Here that would be trading weeds for whatever critter wanted a respite from the heat.

Now, I have used up to six inches that shrinks to about half by fall. I do some weeding but not much. It probably takes me 5 minutes a day with the hula hoe.

Way back when I started gardening, I dumped a lot of mulch thinking it would make things dark so Bermuda grass wouldn't come up. Needless to say it didn't work--it did however make things worse in that department.

A garden that size, you'll overpay big-time if you buy bags. One year I bought four every time I grocery shopped, and I didn't even cover a third of our front garden, similar in size, in a month. (I shop at least twice a week.) The next year we bought a truckload--the bed of a pickup, filled. It gave us a depth of about 3 inches.

I'm curious, why would you want ten inches of mulch?

The places that sell it in bulk can help you estimate the number of cubic yards you'd need. One cubic yard would cover 27 square feet to a depth of 12 inches.