I'm not aware of any Slant/4 GT service videos yet.
Some service items are easier on the GT than they were on the LT, some are harder. But all are definitely doable for a home mechanic with decent skills and confidence.
Changing the air filter is easier, as there's no pulling the fuel tank to get to it. It sits behind a snorkel under the right fairing panel. Also, there's no fuel filter on the GT, so that saves some trouble as well.
Changing final drive oil on the '08 and up bikes is easy with the built-in drain plug. The '06-'07 GTs don't have this drain plug, so draining the FD oil requires unhooking the tension strut and rotating the FD down 90 degrees. A few folks have used small vacuum pumps instead.
Changing engine oil is a little bit more complicated because of the dry-sump engine. You have to snake down a small hose and let the sump drain out slowly. Again, some guys use a vacuum pump for this. The oil filter is accessible outside the engine (instead of under a cover like the LT), but you have to work behind the shifter and it's rotated 90 degrees so it's easy to spill onto the exhaust headers. Refilling requires putting in a bit over 3 quarts, running the engine briefly to circulate the oil through the block, then topping off. Also, its best to check the total level after the bike is warmed up and parked level.
There is no separate transmission housing, so no tranny oil to change.
Changing the plugs and checking/changing the valve clearances is more complicated simply because of where they are on the engine. You have to drain and pull the radiator so you can get the valve cover off. The 4 individual coils sit right on the plugs themselves and can be a slight pain to pop loose. There's also an air injection tube that can be stiff and could break easily if you're not careful. But the plugs last longer, so changes are less frequent.
Once the radiator is moved and the valve cover is off, checking valve lash is the same as on the LT (or any overhead cam engine). BMW's recommendation is to check them every 18K miles. Mine have never needed an adjustment up to 85K miles, but I wouldn't skip these checks as I have heard of a small handful of Slant/4 valves that did need to be adjusted. But for the vast majority of bikes it's just a check only.
After all that, you have to put the radiator back on. This does need to be vacuum filled, so again, that vacuum pump comes in handy. Its not a difficult process, if you take your time and do it well.
Other than that, it's just gas & tires, and the occasional final drive replacement.