Senior digital consultant within a large FMCG firm, including multiple chatbot and “voice first” projects.
Publisher of multiple popular Amazon Alexa skills.
1) Tell everyone about it and gather opinions and criticisms. No one person should dissuade you or boost your confidence in the idea, but a broad spectrum of advice will open your eyes to problems or opportunities you won't have thought of
2) Set up a basic landing page (try unbounce.com or strikingly.com) and set up a low cost Adwords campaign to drive some traffic to it. If you're getting people to sign up for more info that's a good sign, and also gives you potential customers to speak to and learn more
3) Depending on the target market find somewhere you can engage with a bunch of target customers, be that a physical location or a niche forum maybe. Similar to #1 you're just looking for plenty of feedback from the right people
This would give you a good guide on the "demand" side of things. The next step would be to work out if it's financially viable with a big enough potential revenue stream to make it worth the cost and effort of running it...
No one launches with a perfect product. If it's novel and popular then you have to expect others will attempt to piggyback your success, at which point the quality of your team and the deep knowledge of your customers will be vital.
You will have the best usage data and the best access to what is good/bad about your existing proposition via existing users. This will allow you to make smart decisions about the cuts/additions to make to your product, enabling you to stay ahead of the game by delighting existing users and keeping your position as the leading experience in the space.
Ultimately ideas aren't worth a lot, it's honing those ideas into something useful that people are willing to pay for that makes the difference. Plus people tend to be pretty arrogant and have a bunch of (usually terrible) ideas of their own so why would they want to bother with yours? :)
In terms of validating in "stealth" though, if it's a B2C model there are plenty of potential customers out there you can happily share your solution with and have close to zero risk of it spreading any further. You could probably beg them all to tell ten friends each and your secret would still be safe. Trust me, you'll be wondering what you were worried about if you end up proceeding and then have to actually incentivise the distribution of your idea/product!
How much time did you spend with students validating the concept and materials before putting the app together? It's important to know who your target audience is before choosing the appropriate method to reach them.
Regarding the specific ASO side, don't worry too much about the app description beyond the first couple of lines for getting the core USP across. Definitely work hard on your keywords and screenshots though, and keep a close eye on your App Analytics account to see how many visitors you are getting to your page and the conversion rate to installs.
You don't need to spend 6 months on building anything new to validate this. Creating design mockups of another variation that has a white sleek look will be enough to canvas opinions.
It is fairly inexpensive to run a test via google consumer surveys or similar to hit a large chunk of your target demographic with a "which would you buy" type question.
I wouldn't worry about getting it into stores for now. If you success in building a quality product that the market wants you won't struggle for a sales platform.