Use .DXF or .IGES file format for sharing files.
Clearly name the files and if more than one is used then number them in sequence as well.

The file sizes are probably going to be very large so it would be better to list what you have to offer and then send compressed folders to people upon request. There are other solutions of course but may require managing a site like on part of a server someone has, Im not sure.

As for copyright I would suggest that if your willing to put it up on a public forum your making the design public domain and release your rights. Its a donation to the model community.

Also state what software and version was used to design the parts because some have issues importing others files. Having two versions can help like IGES and DXF. This helps when using Solidworks and Pro E for example.
Also an older Solidworks file can be opened on a newer version but a newer file cannot be opened on an older version. This may be the case when trading native files between like software.