I have a 99 yz400f currently that is in alright condition but a bit beat up and way too much bike for me as my first. Would it be a decent trade monetarily to trade for a 2001 cr125 that's in good condition. Mine does have upgraded suspension. His motor was just rebuilt. If it matters this is in Arizona.
First, the "upgraded suspention" will only matter to the buyer if he's the same size as you, rides the same way (fast, slow, etc) and rides the same type (MX, Woods, Desert, etc). AND that all assumes the upgrade was/is actually good.
Second, in your position, I'd make that trade in a heart beat. A 99 YZF unless maintained very well, isn't going to be the most hassle free bike to own. If I'm the CR owner, no way I'd make a trade for an early 4 stroke.