If the project is done the potential on this is continuing residual income for both of us.
Can you give more detail about what you mean by backup your projects?
This question is super vague... I can tell you about backup software, and backup systems if you are just looking to backup your work so you don't lose it in a disaster.
I just am not sure that is what you mean seeing as you seem to want to share income with whomever helps you on this.
What do you mean by "backup my projects"? As a developer you'd usually have some kind of version control system in place (github.com/ or bitbucket.org/), which would also serve as a backup system. If you're looking for someone to keep an archive of your files, there are a number of public or private cloud providers that offer that service (carbonite, ironmountain, goodsync, etc.).
Backups are simple.
Dump your database into a file + create a compressed tarball of your database file + any code files.
Or, if you require hot sparing, run your system in an LXD container + do periodic rsyncs from container to a container on another machine. Then, say once a day, stop the production container + do another rsync to ensure all memory buffers are flushed (database is consistent), then restart production container.
You can also use database replication, so you only lose the last transaction if your production site goes down.
If you're running hot spares, if your production site goes down, you just change your IP to point to your spare + you're back online.