Your guys's opinion on do this repair myself or take it in?

I replaced the serpentine belt and tensioner at the same time on our previous 460 powered coach. It took me just about as long to clear and remove the dog house as it did to do the actual engine work. The total job inclusive took about 30 minutes. Just make a sketch of the belt routing before you start, it'll save time later. I did all of the belt work from the top of the engine. I also did the other items on your list except the thermostat and alternator (done by PO), but not all at the same time.