Good morning, I am in the process of planning how I am going to go about removing the grass from both my front and backyard. Both yards are sloped and with lots of trees. Living in Iowa we get frequent rain and windstorms. My plan is to fill this is with either mulch and or rocks. I am putting in a large garden to fill both yards and turning the front yard into a neighborhood community garden. I want to make sure I am not being rash and will end up doing more damage then good.

HI, Sounds like a lovely goal.
Trees will guide your choice of plants in the community garden. Flowers, shrubs, ferns, moss..

Vegetables don't do well under trees.
I would do it in stages to keep as little bare as possible.
Beware of mulch washing down the slope.
Maybe some slight terracing?

I don't think terracing the woodland slope would be helpful.
Could harm the trees.

You need to tell us how much slope.

I've mulched some pretty steep slopes without a problem, but if there's turf uphill from your yard to send a decent river of water your way... That could be an issue.

We really need to know what kind of water situation you have now.
Consider Swales instead of terraces.

Assuming you are removing lawn/turf? Please consider adding native landscaping--grasses and wildflowers--instead of rocks and mulch (and plastic landscape cloth). Here's a link to some information you might consider:
https://iowastormwater.org/cam...
Much of Iowa was once prairie, take advantage of it!
Also, I strongly suggest touching base with your homeowner's insurance provider before opening your property to a neighborhood garden. There definitely are liability issues!