year end garden preparation
For the past four years I have been amending the soil in my vegetable garden. In the spring I roto till a layer of chopped leaves and horse manure that I put on in the fall. Then, after planting I add another layer of chopped leaves and manure as a weed barrier. After harvesting, I roto till again, turning the weed barrier into the soil. Then I repeat the process each year. The tomatoes and peppers are phenomenal and the soil is rich and dark. My question is, can I overdo this tilling, mulching and composting process? Can there be too much? Should I give it a rest for a year? Thanks for your help.
You should take a break on the tilling. Studies have shown that in home gardens it harms the soil structure and it is usually no longer recommended. See: https://ucanr.edu/sites/Tuolumne_County_Master_Gardeners/files/235827.pdf or https://www.finegardening.com/article/tilling-is-one-chore-you-might-be-able-to-skip. Mulching with chopped leaves is helpful and as they break down worms and other creatures will bring them below the surface without the need to till.
Gardens can have too much organic matter. We tend to think "more is better", but plants also need the nutrients they get from soil. I strongly recommend you have a soil test run next spring (http://soiltest.cfans.umn.edu/testing-services/lawn-garden). That will tell you, among other things, how much organic matter you have and what fertilizer or other amendments, if any, are needed. Continued mulching should provide plenty of organic matter to your soil as well as controlling weeds.