In general, two strokes are considered lower maintenance because there are no valves to adjust. Personally, I find that repacking the silencer (gets all gooped up from the oily exhaust), occasional cleaning of the power valve (it also gets gummed up with exhaust oil) and fouling spark plugs pretty much evens the score.
If you are just starting off on a dirt bike I would not worry about "top end". I ride a YZ-125 and it is pretty rare that I hit my top speed. There is an occasional power line road that my buddies on their 250s just haul down and watch their dust fade into the distance as I hit 6th gear. They wait for me at the end, however, and once we hit the rough stuff I have no problem keeping up. There are a few hills that they climb and I fail but there are others that I climb and they fail.
Mixing the oil for a two stroke is the least of the hassles. I have a little plastic jar with a screw on lid that is marked on the sides for different oil ratios and gallons. The jar cost a few dollars but you can do the exact same thing by taking a jar out of the recycle bin, use water and your kitchen measuring cup to fill the jar and make marks on the side. I emphasize that the jar has a lit because when you are done you put the lid on, which keeps the oil from dripping out or dust from getting it.
You pull into the gas station, fill the jar to the mark, dump it into the can then put in exactly 5 gallons from the pump. If your can holds 6 gallons then you don't have to have the can completely empty. Or just make marks on the jar for 4, 3, 2, and 1 gallons. Very simple.
Two strokes respond differently than four strokes. I think its a lot of fun to get "on the pipe" and feel how powerful and responsive it is. On the other hand, when I am climbing a hill or turning a sharp corner and fall off the pipe at a time when I have suddenly gotten really busy I kind of wish I had a four stroke.
You indicated that you rode your friends YZF 450 so I assume that you know what it takes to kick that beast to life. I have decided that my next bike is going to be a WR450F, but it is going to have electric start.......
yeah, call me a wimp, but most of the cursing I hear on a ride is from someone who is unable to get their bike re-started....
Rod