File Sharing questions

I turned on File Sharing on my iMac so I can access files on my other Macs from it.

1. Is this intended to only be used over my WiFi network?

2. Do I just turn on Remote Login to be able to access the iMac remotely? I'd like to be able to view files on it and maybe copy files to and from it.

3. Under Users there are 3 accounts and I am not even clear where these are from. One is my name and it is listed as read and write, another one is Staff and it was read and write and I just switched it to read only and there is no option for No Access for this one. There is also an Everyone option with it being set to No Access. Are these default users? Can I just delete Staff and Everyone?

Thanks.