BRO250R's are great bikes with a little work.
First thing you should do, is set the sag.
its free other than your time and it needs to be done.
https://www.youtube.com/watch?v=ns4pJO7zyHg
Next order of business is some protection for the bikes vital parts, skid plate, radiator braces, hand guards, pick up an hour meter and a spare air filter while you're at it.
As far as the stalling, this is a mx gear box so 1st is going to be a little tall, you can gear it down, but just remember theres always a trade off, if you gear it lower you won't have the top speed or the run out in each gear, but thats dependent on your riding set up, I would suggest that you leave the front alone and go bigger on the rear as the effect is less drastic.
Another must is a spark arrestor, rather it be an end cap or a new muffler, the end cap is cheaper, and a muffler won't gain you a lot.
http://www.btosports.com/p/Pro-Moto-Billet-Spark-Arrestor-Endcap-Honda
The other thing you need to do is post some pictures here.