On the mask, I'd suggest an E-Flex. Lightweight, easy for him to maintain, low profile yet lots of protection and airflow. That being said, get a second strap for it, put that on in addition to the first. It'll ensure a super comfortable and secure fit so there's no way in hell it could fall off. I still double strap all my masks.
On the tank, get the measurements for various tank sizes (varies per company) and get something of equal length and put them up against his arm to see which will reach from his shoulder to his elbow, then pick that size up
I'd think a 48/45 or 50/45 (both with a regulator extender) or a 45/45 would do the trick fairly decently for him.