Most commonly kept semi aquatic turtles ie sliders, painted turtles are omnivores, so they will eat plants. Painted turtles are smaller, so would be a little less destructive plant wise. As for bringing them in during the winter or letting them brumate in the pond depends on your climate and how your pond is set up. They don’t need to bury in mud, but will want to tuck under sunken logs or under large rocks or caves for the winter. Just pay attention to them as they come out of this period as they can look a little rough and may need a little help in recovering.
Watch out for predators even adult turtles are still prey to hawks, ospreys, eagles etc. and as was mentioned your pond will need to be escape proof ie a fence or raised vertical sides on the pond. Turtles are excellent escape artists.
I have kept Diamondback terrapins in my outdoor ponds for 12 years and leave them out there year round. These turtles are strictly carnivores, so they leave plants alone. The only catch is they are naturally brackish water turtles, so if you wish to keep them in freshwater they must be raised in it from a juvenile and the water must be kept clean as they can develop skin/shell issues otherwise. My ponds were designed with turtles in mind, so there are plenty of places for them to brumate.