*Would it do any good to treat with beneficial nematodes now? (I've heard that only does good in the fall?)

They work all year long as long as the soil temp is above 50 degrees F.

*What is the best place to get these nematodes?

I like this place.

*Should I treat with milky spore instead, or is that only effective at certain times as well?

In the north milky spore seems to be a better choice. The problem with that is you didn't start five years ago and apply annually.

*Do the "chemical" grub treatments found at places like Lowe's, etc. kill off all bugs?

Yes.

But before you do anything, dig up one square foot of soil somewhere. If you do not have a dozen grubs in that square foot, then apply something. Otherwise, leave well enough alone.

Thanks for the advice and the link.

"If you do not have a dozen grubs in that square foot, then apply something. Otherwise, leave well enough alone."

Did you actually mean if I do not have a dozen grubs in that square foot, don't apply something? I wanted to be sure...in the meantime, I'll do some digging!

Yes. If you don't have more than a dozen per square foot, you don't have a grub problem. That is they eat so little your grass can recover and you'll never notice.