You stole it. :thumbsup: Typical price for all that, at least over here on the left coast, would be 2x~3x what you paid assuming good condition.
I have a YM186D. Same thing, US version. I can't think of any tips. These things are pretty obvious.
You are doing the right thing to replace fluids upon buying it. Don't overlook the transmission 'strainer' behind the triangular plate. You might drop the fuel filter bowl and see if that filter needs replacement too, but this doesn't need to be done immediately.
And consider replacing the front axle fluid. 90 wt gear oil, and there are drains at the lowest points of the hubs. Expect overnight to drain completely, and hours, maybe days, for a fill to settle in so the little dipstick (right axle) means anything. Measure the quantity that came out, to estimate how much to refill. As I recall, mine need at least two quart jugs.
These all need the radiator exterior fins flushed clean with a garden hose, to get rid of mowing chaff.
I have water
ballast in all four tires, 250 lbs on the front bumper, two 70 lb iron weights on the back wheels, and a 70 lb Quickhitch out back. It still has more hp than traction.
Welcome aboard!
