Plugin suggestion(s) for managing ongoing data for users

I'm wondering if anyone has any suggestions for a plugin (or plugins) that might help me. I'm running a site for a client which was set up pretty hastily and I'm trying to see if there's a better way of handling it.

The site is for an annual convention which has both individual speakers and organisations who exhibit. At the moment I'm using Ninja Forms to collect information from people/organisations and give them the means to upload files (photos, PDFs etc.).

This has worked OK but there are some downsides. When the next convention comes around people will have to fill in all their data again rather than using the previous years info as a starting point. Also, individuals/organisations have submitted data across multiple forms and so the only way to see all the data for one person/organisation is to look at multiple form submissions.

Does anyone know of a kind of membership plugin that would allow an individual/organisation to login to a central area where I could then create custom forms to collect data/files such that on the back end we could look and see all the info for one user in one place?

Hope that makes sense – anyone got any ideas?!