More than voice, singing effectively needs control, and expression. If it were all voice, people like Dr. John, Stevie Nicks, John Lennon and so many others wouldn't have 'made it'.
I'm a multi instrumentalist who had to learn to sing. As bands downsized to make a living, I found myself in a duo
http://www.s-cats.com with a very good singer. But she couldn't sing all the songs all night, and what if she got sick? I figured I'd learn to sing.
I started singing the easier songs, and worked up to more difficult ones. Since my duo partner is a far better singer than I'll ever be, she sings the hardest songs. But I play sax, flute, wind synth, guitar, bass, drums, keyboard synth, and make our own backing tracks. We both have different strong suits that complement each other.
Learning to sing for me, expression wasn't a problem, because I am a very expressive sax player, and it's similar. Breath support was OK because it's the same as a wind instrument. (Breathe with your diaphragm not your chest, keep your throat relaxed, and tighten the muscles of your abdomen as if you were expecting someone to punch you there, and so on).
The hardest part was control, to sing on pitch, off pitch intentionally for expressive devices, and so much more. It took a lot of singing to strengthen those muscles to the point where I could get them to do what I want. Without the control, the expression was not possible.
I know a few people around here who make a living singing to karaoke tracks. They sing in smaller venues, private parties, and so on, and seem to be able to support themselves. That's a possibility for you.
Whatever you choose, you need to sing a lot, every day, start slow, so you don't injure yourself, but end up singing for hours per day. Take at least enough lessons to learn breath control and how to breathe properly. If you don't, you can get nodules on your vocal cords and end up with a raspy voice like Ms. Nicks.
Practice, practice, practice. Sing along with recordings of successful singers. Notice the subtle things they do and mimic them. A few examples are phrasing; singing some notes ahead or behind the beat. Pitch deviations, including singing a note a bit flat and pulling it up to pitch, controlling speed and intensity of vibrato, changing the shape of your oral cavity to color the notes differently, and so on.
You also need to see what works in your area. Is country big? Classic rock? Anything else? Check out your competition, and see what they are doing. Watch the audience and see what is working and what isn't working so well. Learn from their successes and mistakes. How are they dressed and presenting themselves? Again, what works for your area and chosen genre.
I am a career musician. It's not easy, although I'm on stage only 3 or 4 hours per gig, I put in well over 40 hours per week working. It's my passion, so it doesn't seem like work. But it takes practice, constantly learning new songs, pushing my limits so I can sing more difficult songs, hitting the streets to promote myself and find new gigs.
Singing is one of the easiest things to do. It takes no work or skill at all. Singing well enough and singing for a living is a very difficult thing to do. It takes countless hours of practice, plenty of time to put in and good off-stage skills, too.
I probably put in 70 hours a week doing what I do, but because it's my passion, it doesn't seem like work, it's just involvement in my trade. I've had two 40 hours per week jobs in my life, and for me, I'd much rather do this. Of course, that's just me.
If you want to make a career doing music and nothing but music, dedicate yourself to it, put in the time. If you have the inborn talent and develop all the skills necessary to do it, you can make a living doing music and nothing but music.
And as others mentioned, it would help to learn a musical instrument, too.
Insights and incites by Notes ♫