I'm very sorry to hear you have lost Sunny. He sounds like a real character and the space he has left must be vast. My Dad kept birds, in fact he was a champion breeder of several varities and was sought after to increase endangered ones. I witnessed him cry several times after the passing of one of his favourites. He had many pets over the years, Growing up I believed we lived in a zoo or at least thought everyone else was surrounded with as many animals and birds. I learned from him that the bond was equally strong for anything you cared for. A bit like you he reduced just how many birds he had due to age. When his health started to fail I saw rhe sadness of having to reduce numbers and not be able to replace them. So I totally understand how you feel. What you did for Sunny speaks volumes. You fed him and held him, eventually easing his pain. That's love.
Religious or not I think you can be pretty sure there is a heaven for all. If anything deserves it then it is those little things that have brought happiness without question.
I'm sure you have some lovely memories of Sunny and I hope they bring you peace.
Love you forever and ever and I will be there for you xx