This much rust repair is made a lot easier with the availability of replacement panels, but some stuff has to be made by hand.
The firewall is one of the simpler areas, due to the large flat real estate it comprises. The tight work space in some spots can make a guy grumble a bit, but there is nothing too complicated here.
Still, even simple tasks require planning and patience. Using the brake to make these bends, if you're not careful, you can bend yourself out of position, and end up blocking where you need to be for another bend down the road.
So a bit of head scratching should take place first to make sure you don't shoot yourself in the foot.
To go slow is to go fast.