About him being with other fish, dragonscales tend (not always, though) to be on the more aggressive side. I would wait until you have him eating (stress, depression, probably some minor ailments also) and have a good idea of his personality. He may be carrying something and you wouldn't want that transferring to your guppies. Give it a month or so and then try by floating him for a good while in a cup so he can see them for awhile. Then, add him in. Keep a net in hand. He may attack or the guppies may nip.
For a dragonscale especially, you should look into some high quality pellets. He is a gorgeous fish and if you get him on a good diet, he will just pop with color. Flakes really aren't the best when it comes to nutrition and they also are a lot messier for your tank in general. I would encourage you to look into things like New Life Spectrum, Hikari, Omega One, etc. I personally use Hikari pellets currently and have seen a great increase in color/energy/health of my bettas. Also, freeze-dried blood worms should be used only as a treat. They do not give much of anything to your fish and the freeze drying process pulls out most of the good stuff. If you want a treat (a little once a week or one every two weeks) then go for some frozen bloodworms or some live small ghost shrimp.
It's is for sure a male. Petsmart normally does not carry females in anything other than veil-tail and crown-tail for the most part. It will get more used to you in a few days/weeks. Just make sure to always slowly walk up to the tank, making as little vibration as possible. He will warm up soon. Just takes him to get over the huge hump of what he was subjected to before you bought him.
Good luck!