I'm in my 30s, and I'd be open to participating to give you feedback, but I am not sure if I'm your target market.
I'm not that interested in a 0-500 type challenge because I'm past that. I think most people on this forum are. BUT, even when I was paycheque to paycheque, I didn't see it as 0. Sometimes I had 0, sometimes I had 700, sometimes I had 2000. I needed help figuring out to get that to 500, 1200 and 2500 without self-sabotage. I would never have seen myself as having 0, and would have happily given money and advice to people claiming to have 0.
I also think that getting to 300 or 500 in those timeframes might be too much for your target audience, without making more money or moving homes. Talking in percentages might help. The only way I can imagine hitting those numbers is by doing the ERE challenges, which are too tough.
My last weird thing, is that I'd love if a challenge like this had a habit survey before the automated emails. That way, if my coffee and lunch budget is down to 0, you can still send me a list of habit changes that will help me meet my goals. Harder to automate, but more valuable.