Is there a reason for adding the ph powder? From what I read, it's best not to use ph + or - additives, unless the ph is way out of control, since it's harder to keep the ph level with additives than it is for the fish to get used to slightly higher or lower than their preferred ph parameters. Something I'm learning about bettas - they hate sudden change!
I live in Australia and where we live I get room temp variations this time of year from a max of 38C (100F)to 17C (62F) at night or lower, so I -have to- use a heater to keep the temp steady. The thermostat turns off when the water hits 26C (78F) so I don't fear overheating. As long as you have a thermostat, it should all be fine and you won't risk cold fish in case of a chilly night. 72 is also a bit cold for him...
It sounds like you're making an excellent home for your betta.
Don't worry if he seems a little depressed or won't eat in the first couple weeks of his new home, they hate adjusting and take time to get used to the new water and so on.
Good luck with him, and I'd love to see some pics. :)