I like the song, and I think your singing is just fine. I agree, there is a little Roy Orbison sound here, and that's a good thing! The arrangement is good, and your guitar work is not bad. The mandolin was a little out of tune - but that's not always necessarily bad. Sometimes I will use instruments purposely slightly out of tune to bring a fuller sound (that's in essence what a chorus does, in some settings). I would move the mandolin back in the mix just a little bit, so it doesn't dominate, and prove how out of tune it is.
(My main "studied" instrument in college was violin, so I love the mandolin.)
These are just nit picks, but you are doing a good job! Keep working on it and you will always improve. When it comes to mixing, it just takes a lot of practice, and really, really, really using your ears! Don't do any final mixing at the same time you recorded, your judgment will always be impaired by your "favorite" part, not to mention your ears will most likely be fatigued after recording. (That's a mistake I still make, out of excitement for my "new creation".)
Again, keep up the good work! It's always fun to create, isn't it!