Checklist:
- Checksum validation (CRC, MD5, SHA1, etc.)
- Bandwidth limit
- Host's TOS (abuse of services)
- File review (malware, backdoors, etc.)
- Upload method (how is it uploaded, reviewed and checked)
- User Responsibility / User Liability
- Your TOS/TOU for your service
You're asking for a lot of work to be done. So, either you need someone who really wants to learn about all this stuff and is dedicated to the project, or you pay someone who knows what they are doing and set's it up properly. Otherwise, you're looking at a lot of misuse, because there are people who will use this to infect others, publish bad files, and so on. A lot of games will kick a client if their file does not match the servers. So while the file may be similar, it might differ slightly and still be a valid non-malicious file, but will still kick clients. There's a bunch of other stuff, but this is only the first step to getting a site like that up and running without a lot of potholes.