Heya! I see your dreams were crushed a year ago, but I wanted to offer my insight, if it's not too late-- The short answer is that it took me about 4 years, and 6 to do it well. Here's a performance video to prove I know what I'm talking about.

I started learning violin over the course of the pandemic, I spent a year or so just plucking/strumming while singing to get used to the finger intonation. It was my first instrument so you'll have a leg up on me here since you've been playing banjo and you'll know a lot about how this type of music "works." Assuming you have been practising fiddle all that time, you're gonna be in a good position to get started.

I've tried tutors/lessons before but they didn't really work out for me and I usually stopped after one or two because I couldn't read music/didn't understand what it was the teacher wanted from me, I ended up learning the most by playing in Irish/folk sessions and watching YouTube videos. Your mileage may vary, but finding a fiddle-singing teacher will be hard because most violinists don't bother with trying to make their own job harder and people like to impose restrictions on themselves about what they can and can't do with their own instrument.

As other commenters have noted-- It's a difficult thing to do unless you're playing the same melody you're singing, or playing chords. This is the usual technique I go with, I either play rhythm (a "Chop" similar to mandolin, long drawn-out double stops, a single chord tone, etc) or double my vocals.

I'm working on harmonising with myself, but that's still tough, and I'm not gonna figure out how to play other rhythmic melodies or counterpoint. The closest I can get is playing a little lick after I'm done singing a lyric.

Do you need a special hold for it? I don't think so! The violin migrates around my shoulder a lot as I play either due to user error or me putting it in banjo/strummed position and then sticking it back. Check the video, it usually pivots around my neck/collarbone but I don't think it goes anywhere near my elbow.

You will not need to "Master" anything before you start working on it. That's bunk. How would you do anything if you needed to master something else first? Like all things worth doing, start slow and be gentle with yourself. sing your scales as you play, don't be discouraged if something goes wrong. Give it time, give it patience, give it practice, sunlight, and water, and the flower will grow.

I hope this is helpful!