You could upload data to storj directly from the browser, but that would mean to expose secret information like connection data and encryption key. Since this data is delivered to any connecting users browser, it can be exploited.
So you need something where you can send your data to which accepts your file and forwards it to storj while keeping the storj credentials hidden.
Depending on the programming language and your skills you can proxy the file through your server without storing anything there. It’s not really unneccessary complexity. If you want to connect to a database you have the same problem.
As for performance it depends on how many users you have at the same time. The main issue is internet connection speed. There is also some processing necessary for the encryption process or you can use the public gateway which does the processing for you.
You could use some cloud functions like google cloud functions or aws lamda or vercel to run you server, doesn’t need to be a full fledged hardware server.
Hope that helps.