Yeah, not the friendliest platform for oil changes. Before I got the Drainzit, I had to remove my engine for every oil change because there's no clearance in my bike's small frame with a shift kit mount. Even unscrewing and removing the dipstick on my setup requires great patience. Some people use a vacuum pump rather than draining the oil because it's more convenient and less messy. That leaves more used oil in the engine case then I feel comfortable with, but it seems to work fine for those that use a pump.
IMO, 5w30 is too thin, but it most likely is just fine. These little industrial engines are made to run on straight 30 weight; thicker oils have more shear strength, but thin oils are better for fuel efficiency and power. 10w30 would be the thinnest oil I'd recommend, I run 15w40 Shell Rotella on mine. It takes a quarter of a quart, so 8oz.