Last year I bought a used compost tumbler & have been putting coffee grounds, left over kitchen waste, occasionally left over potting soil. I was finally able to mow 3 or 4 days ago before it started to rain again. This is bahalia grass. Can I still add these clippings to my compost? This is ALOT of clippings because it was about an acre & the grass was THICK. How do I know when I've added too much?

If you have Bahiagrass, don't turn around! It will need cutting again by the time you do.
You will have way more grass than you can put though a compost tumbler. But grass mixed with other materials and heated up enough to kill those bahiagrass seeds will be great. It does not take a lot of grass mixed in to heat up a pile, and you know you have added too much when the smell is bad enough to keep you from wanting to work with the compost. With that much grass you will not be able to use it all in a compost tumbler. If you have an out of the way area to make a large pile and you are physically able to work it, then you would have an excellent source of green materials for your compost pile. If you are not able to work it, then just pile it up in an out of the way spot and come back next year, and harvest the remains.