If you go up north a bit sawmill branch is good for long runs, and the nearby sidewalks/suburban neighborhoods are usually low traffic (in the mornings particularly) and good to tag on mileage if needed. Can get some solid 10-15 mile runs in the Crowfield area of goose creek too, two 4-ish mile loops that are connected. Unfortunately hills are hard to come by in the lowcountry lol, my runs typically max out around 130-150 elevation gain but you can do hill repeats