The heat is unlikely to kill your herbs - my garden here in the fierce heat of the subtropics attests to that! If you're using your herbs enough, you don't need to do much more trimming. But you can do it at any time. Rule of thumb is to take off no more than one-third of total growth at any one time. My mints are happier in partial shade. Just make sure you keep the soil consistently moist (which doesn't mean soggy).

You coriander will bolt to seed once the heat hits it. It's too hot for it even in winter where I live. Let it go to seed, because that way, you'll ensure a constant supply of the leaves, once the patch becomes well established.

I don't know of any herb that you can't freeze. However, some, like parsley, and dill, will be limp on thawing, so no good for garnishing. You can freeze herbs in an ice-cube container, but I prefer to put them into a plastic bag and make a thin, flat pancake of it which can be easily broken off in required amounts. No talent, no special skills required.

Plenty of pesto recipes have been posted here before. Mix up your leftovers into some sour cream or yoghurt or cream cheese to make a dip or spread. Or put a spoonful onto baked jacket potatoes. Stir some into your veges, meatballs or meatloaf, or use it as a sauce for them.

Here is a link that might be useful: pesto

Sage is the one that will keep as much flavor dried as frozen. Dill is close. Cilantro and parsley are useless dried.

I think you might be worrying over nothing. They should all survive the summer heat, if not thrive in it. The cilantro will bolt like crazy, though... And in your climate, I'd actually suggest E. Foetidum, which tastes almost exactly the same, but doesn't bolt like crazy in sub-tropical climates, and doesn't die back as far as I know. It's a slow starter, but I've had plenty of sucess growing it in an east-facing window. Also, the parsley will be a very slow grower during the summer, but should really grow during the cooler months.