Your dragon is beautiful!
when i got my bearded for the first time i wasnt so clear on the staples. i used to feed him mealworms..i know baaad choice lol but i didnt know any better.
after i awhile i switched to pheonix worms and waxworms as treats and stuff because he became a little underweight.
then not to long after that i switched to hornworms. once i finish those he became over 15" and i went to supers.
honestly i gotta say in my experience using supers its really great! they are very good for them. he goes nuts for them! but once in awhile ill get him crickets from the petstore. i only feed them as treats because its too expensive to go back and forth to the store and they die to quickly when you try caring for them. anyways he never refuses them he would gobble them up!
now im starting my own superworm colony which i suggest for anyone who doesnt have a lot of money to keep buying worms to do. you save ALOT of money and you have unlimited supply of worms at all times. once you get the colony going. once you get that going youll be able to buy different worms. like butterworms,silkworms,hornworms and etc. these are great for variety!. since your beardie isnt 15" id stick with soft bodied worms like pheonix worms,hornworms,silkworms and etc.
you can actually start a colony now before he becomes 15" so youll have them ready once he becomes big enough!
once your beardie realizes that what you give him is the only option he has. he'll eat it!
as far as the pooping thing im going through poop issues with my beardie as well.
the way your describing his pattern of pooping if im not mistaken its almost like how they start to poop once they reach adulthood.
im not an expert but i remember reading that once they reach to be an adult they only poop once a week. my beardie poops every other day now. so im guessing hes getting there.