Aggregate can certainly handle that many submissions. There a few known limitations that are unlikely to affect you, but are worth reviewing. Are you planning to self-host? As noted in the docs, using Digital Ocean is recommended. If you want to hire help, there are a list of people and organizations listed on the providers page of the ODK website.
Without seeing your forms, we can't guess if there might be any issues with the survey design. I would definitely suggest that you test your form many times with different users. This testing will hopefully catch any possible mistakes or bugs in the form design. You may also want to develop additional guidance documentation to help explain the process to the people filling out the forms. Something like a 1 or 2 page summary or checklist or tips document.
Testing your form will also give you some demo data that you can use to test your data analysis plan. It would be good to plan how you will analyze the data before you deploy your form. Things like groups, repeats, and other form design decisions can may it easier or harder to conduct your analysis.