There is not enough information to form an opinion on your particular situation, however, I can tell you this:
Submitting a sitemap will not effect being banned or not. With 1 million pages, you should be submitting a sitemap.
Google does not like thin content and that is what you are saying you may have. Find ways to fill in your pages especially with value added content. What can you do that your competition does not or cannot? This is your value add. Just doing what everyone else does will not save you from being banned, but adding valuable content can. Perhaps a review option so that users can rate the download and possibly leave comments. Perhaps you can review some of these downloads yourself or make recommendations. But I must make one warning, if you are hanging your hat on user activity and your site does not add value, then user participation may never come. You have to do something to not only engage your user, but encourage and compel a user to want to participate in your success. And that is the secret. The web is a win win scenario always. You give something and others will give back. People want to reward those who have helped them and they feel compelled to help.
Even if you do not add value or get banned, thin content will place you very low in the SERPs. And that is an important fact. Thin content cannot succeed either short-term or long-term.
Here is the rub, I am not sure what the value of your website is, you know best, but if it is created for humans and is helpful to humans, then you should be okay. If you are creating the website for search traffic and the metrics that align with user satisfaction and usage are low, then your site will fail and there is nothing you can do about it except to rework the site. So get it right now rather than fighting to gain traction with a site that has no traction. This can take a year or more. However, a valuable site will only go up in traffic and performance if you work it. And it is work. There is no such thing as easy or free on the web. Keep that in mind.