Depending on the campground will determine how long of hoses you will need.
You can get a clear elbow for sewer flush if you want. Sewer hoses come sectional, the campground we go to the most we have 25 feet worth. Buy a decent quality hose don't buy the really cheap ones. We are currently using Rhino but other brands are good as well. As far as hose supports there are several styles. As you camp you will see more as to what others use.
Same with water buy a decent quality hose not a cheap one. For sewer flush quality is not as important. When putting your hoses up hook the ends together so nothing crawls in.
Some campgrounds the hookups are toward the back of the trailer some are in the middle. Some further away....... There is no standard for where hook ups are.... And many campground do not have sewer hookups so a dump station would be used for waste water.
It is hard to say buy a x feet hose but for most places 25 feet is rule of thumb (my opinion) some places may need more some less.