I have mixed thoughts on this issue.
A certain amount of girth is helpful for hanging because it allows more adjustment of the hanger and provides more gripping area. I don’t know how much is ideal, but at 4.75” erect, I’d prefer another 1/2” or so to make better use of the adjustments.
For many guys, me included, girth is much harder to come by than length. Delaying girth worth until after your length goals are met may greatly extend the PE process.
Doing both at the same time may work synergistically. In my case, I’ve gained some length from what was supposed to be a girth-oriented routine. Blowing it up and then stretching it out may be better than just stretching it out.
OTOH, I find it difficult to do both effectively at the same time. Girth work interferes with hanging because of fluid buildup and shaft soreness. As tempting as it is to do something for girth, I try to leave it alone when I’m on a dedicated hanging schedule.
Alternating length and girth may be a good way to go. Allow the ligs to decondition while hitting girth for a few months and vice versa.