Disclaimer - I'm NO expert.... but...
I'd just like to say +1 for American Supercamp!
One of the best classes ever to learn how to ride and control a bike off road
AND on road.
I'd also say you could, if you wanted, just do some easy mods and tuning to that YZ and have a great (and easy to ride) bike. But the 250 4-stk is not a bad idea. I just love my 2-smoker
Also curious how you hurt your foot... did you have on solid protective MX boots? Those generally prevent damage even during pretty bad spills. Generally.
Other than that... get the fleshy bit atop the bike in shape! I highly recommend Mt Biking and Kettlebells for building up the strength and endurance needed for off-road riding (or serious on-road riding).
Good luck!!