At 50 hours, I switched my engine oil to Rotella synthetic 5W-40. I just drained, installed new filter and the synthetic oil. I used the synthetic on subsequent oil changes every 100 hours. Some members go 150 hours on synthetic. The engine has been fine with the 400 plus hours I have on the meter now. Others have many more hours than that. I wouldn't worry about doing a flush. With only 50 hours, you don't have any crud built up. About all you will see with the oil is a little pearl like sheen to the oil which is from all the new moving parts mating in.
If you are going to use Amsoil synthetic hydro fluid also, their site advised that you can go longer on change intervals, I think double, before a drain and fill. I would hope so because it costs twice as much. Normally it's every 200 hours for filters and hydro fluid is at every 400 hours. You'll probably want to still do the filters at every 200 hours but may be able to go to 800 hours before changing the hydro fluid. I did my first hydro change at 50 hours by the manual and of course, it looked new. When I changed again at 400 hours, it still looked new. Depending on your weather and temperature, I would just watch for any condensation and water retention in the oil.
If your handy, the engine and hydro oil changing will go fine. Partiall fill the engine oil filter and put some oil on the filter gasket before you install. Remember, there are two drain plugs in the engine oil pan. The hydro oil isn't much different other than you will have to catch @7.5 gallons of fluid. Fill the filters before you install. You will have the main drain plug in the center of the trans area that I open first. When almost empty, there are two drains at each end of the rear axle.
