I’d say do tbelt first, run it before putting the covers back on, if it runs right, put all but the front cover back on, leaving it off makes it easier to see the cylinder marks on the cam sprockets when doing the valves. The rest is dealer’s choice unless you wanted to maybe do the valves and back plugs, put it together run it and if it’s okay do the front plugs.. that way if you goofed something you got an idea what it is.. that’s a lot to do in one whack.
I just finished these jobs. It's a lot for a 3-day weekend unless everything goes smoothly and you don't need to stop to think about what to do next.
I did the valves first. It's easy to see the timing marks through the porthole, especially with a small mirror. You can take off the front upper cover if you prefer. Either way, rotate the engine from the power steering pump pulley bolt and watch them come around. When you get the head covers and throttle body back on, you can check and see if its running quietly for five or ten minutes because you haven't dumped your coolant yet.
That also gives you an opportunity to punt on the timing belt for another weekend if the valve job expands - mine turned into an EGR cleanup as well.
Doing the t-stat with the throttle body back on is a little cramped, but doable. I did the upper and lower hoses at the same time. You can replace your air filter before you put the air box back on, then start on the timing belt with the coolant (mostly) already drained.
I did the accessory belt and power steering pump belt while I had it apart. That doesn't add much time to the job, and you re-start the clock with new belts and tensioners all around.
Forgot about the thermostat component.. how’s the radiator? And equally importantly if you’re in the rust belt the steel transmission cooler line at the bottom of the radiator. Both my rad and line were junk when I bought the 08.