Yep it'll work but depends in which format it's in, if NTFS you would need a third party app to write to it,if FAT32 then yes you have both read/write access but are limited to 4GB file transfers
Yes. Likey you can just plug it in and read the data on the drive. But if you intend to use it only with a Mac then you will be best off to re-format the drive with an HFS+ file system. If the drive is to be shared with a Windows PC then your need to use fat32 file system. Use Disk Utility for this.