Thank you so much for the update. I am so.....glad that you have a betta now and can finally enjoy him. Yes with betta you never know he might be fine with other fish at the beginning but always can get aggressive when he get adjusted and comfortable in his new home. Do you have any questions about water changes? If you cycling your tank i can give you very good link about cycling and cleaning filter media, and water changes. If you don't cycle i also can give advice on water changes. My bettas are old, one is almost 5 years:)
Good luck :) Thank you.