Leave the old mulch to continue to decompose and add more mulch right on top of it. It will enrich the soil and you won't need as much new mulch.

For fruit trees - you should spray lime/sulfur before they leaf out. If they have leaves already then it's too late. I don't spray for insects. I'm going to try bagging my peaches this year with shoe store try on footies. The little nylon footies are supposed to work well to keep the insects off without spraying.

I don't know anything about grapes. Check the fruit and orchards forum and you should find something on it.

Keeping away rabbits requires a fence and two dogs. At least, that's all that has worked for me. If you want to try a spray, try Liquid Fence. Reapply it after it rains. It works fairly well if the rabbits aren't too hungry. Otherwise try planting smelly or poisonous plants. The rabbits aren't likely to bother those. I don't have any experience with deer so I can't offer you advice there.

I grow hot peppers & dry & grind up the leftovers to sprinkle around plants in the Spring to deter rabbits & deer. There is a commercial product called hot pepper wax. Both help most years but if the critters are really hungry, only a fence will do. I fight the battle with deer & rabbits & my tulips every year. A hawk got the neighborhood rabbit a few weeks ago so I may see blooms this Spring.

Great idea for the peaches (and other fruits)! Do report back in late summer.

May be more than you ever wanted to know about grapes, but look here:
http://www.extension.umn.edu/distribution/horticulture/DG1103.html