Finding the best keys to sing in and singing in tune!

Aplogies if this this like a re-hash of John's previous post in this group but I couldn't find the blogs and vids John referred to

Ive no musical background and feel a mental block coming on when I start thinking/reading about scales and keys but I know its something I will have to get my head around properly if I'm going to improve

I like playing in Ddd (Is that G?) and Ead or Ebd (A minor?) but I think Ddd is too high to me to sing to

I think part of the problem is I don't have a very good voice to begin with so sometimes working out if I'm in the right key is difficult when I'm out of tune anyway.

Ive not done much singing on FOTMD. Darlin Cory which was played in Ebd I think but I'm not sure what key I sang in! The other was 'Portrait of my Wife' which I sang and played alternatively because It didnt sound right when I played in Ddd and sang. I was tuned Ddd but again I'm not sure what key I was trying to sing in.(By the way if anyone wishs to refer to my singing on this site you have my blessing to be a honest as you can be)

Any tips or advice would be appreciated including any tips on singing in tune