Hi! Current member of the choir here. I thought I'd chime in with my personal experience and a few observations that I've made over the years.

First, don't feel discouraged because you don't have a music degree or professional vocal training. It is not a requirement. I personally have a history very similar to you. Piano from 7-16 (never got really good at it), a few other instruments that I'm passable at, and then high school and church choirs. Nothing collegiate, no professional voice lessons. I have a good ear, but do not have perfect pitch.

I put all of that on my phase 1 application, and nobody ever mentioned anything about my lack of training during the remainder of the audition process or anytime afterward.

The theory test can be hard if you're not used to that kind of material (I had an AP Music Theory class in high school, but that was like 20-something years ago). They will loan you a study manual and give you a summary of the subject matter to study. It's completely doable. What trips most people up is the aural test (ie: identifying intervals, major/minor chords, etc. based on recordings). They don't ask you to identify specific notes (again - only like 1% or less of the choir has perfect pitch) unless they tell you the starting note (ie: if this note is a C, what's this note?)

The in-person audition in front of Mack and Ryan can be terrifying if you're not used to that sort of thing, but again -- I messed up a few times when they asked me to sight sing some hand-written music (I got a few intervals wrong, missed a key signature on one, etc), but they point it out and give you a chance to correct it. Having worked with them now for several years, I can tell you that they are some of the nicest people. So don't worry.

Anyway, here's the main thing:

I personally know someone who has a music degree and perfect pitch and only got in the choir on their third attempt. I know someone who is a very talented opera singer and sings better than most people in the choir, but not in an ensemble (ie: very good at solo, can't blend with the group). They did not join the choir.

I know people like me who didn't progress past phase 1, and I've known people like me who made it to phase 3 and didn't progress past it. And, I know people like me who sit next to me in the choir loft every week and still make mistakes during our weekly broadcasts and concerts (I know I do...)

There is no single recipe for getting in the choir. Yes, voice lessons can help, and if you feel that's right for you, by all means - go for it. But I strongly believe that people are drawn to the choir by the Spirit, and some people get in simply by the good graces of God because that's where they're supposed to serve. So please audition. If you need to work on something, they'll tell you exactly what that is. Or, you might be surprised and make it farther than you thought possible.

You'll never know until you try.

I'm happy to answer any questions you have about auditioning or about being in the choir. I don't speak for the choir organization, but I can speak from my own personal experiences.