I have an Ortlieb Ultimate 5 Plus handlebar bag. The bag is fine, great even, but the mounting hardware is poorly designed IMO. The mount holds the bag securely, but it's made to be installed once, so it lives on your bike forever. It attaches by threading a special cable between the mount, handlebars, and stem. Screws then tighten the cable down. It's solid, but because of the way the screws damage the cable, it's not practical to take off and put it back on again. The mounting hardware takes up a lot of handlebar real estate needed for lights and other things. If you're set on the bag, go easy on tightening the screws to not damage the cable too much. As for lights, I suppose you could use something like
this to mount your light along your front axel.