...and Basil, if that matters.? Also, it won't be effected too much by adding other things, right? Such as grass clippings with it?

grass clipping are good, and eggshells. I don't think coffee will do much.

Yea I think it makes a great mulch. I have used it in the past you plant will come out looking healthy and so good.

The best thing to use as mulch for plants is compost, which is a mixture of everything organic, or biodegradable, that has broken down into soil, or mulchy stuff. This can be anything from grass clippings, coffee grounds, to things like old veggies and fruits you found in your fridge, they all add different nutrients for your plants. Too much of something, like coffee grounds, might throw off the balance of things by having too much acidity or other things added by factories, but again, mixed with other things, they will work just fine. Our family has a special scent-sealing compost bin in our backyard, and we just throw anything in there. there are things specially made just for composting. It also reduces you garbage amounts too.
We use composts in our gardens and the plants grow tall and produce lots, including bell peppers and basil.