Go only works on your iPhone so it can't "send a file to your iPhone". You can use iTunes or Drop Box and (I believe) iCloud to copy a file from your lap top to your iPhone. iTunes can "save" the copy on your iPhone back to the laptop and some users email a copy of the database to themselve from their iPhones or so I have read.
You can also open your database on your laptop and use WiFi or 3G/4G to wirelessly access the file hosted on your laptop. This requires setting things up fo sharing and the file must be open on your laptop at the time. Your part time worker could also access your hosted file via WiFi or a wired network under the same circumstances.
If you plan to distribute a copy to your worker, a File created on a Windows system can be opened without major issue on the Mac system and vice versa. Some layout issues are less trouble if you initially design in windows, then copy the file to Mac as windows systems need a few more pixels to display the same size text. But managing the updates needed to merge the data created/modified by your worker with the copy on your laptop and perhaps a third copy on your phone could range from simple to very complex depending on the structure of your database and how the database is used. Of particular concern is if you modify a record in one way on the iPhone copy, your worker modifes the same record in a different way on their laptop and then you sync both copies back to your copy on the lap top. Can that be done without losing one of the two changes? Don't know, but ther are two third parties: SeedCode and 360Works that offer sync tools for this purpose that you may want to investigate. But avoiding the need by hosting your files--which does not require purchasing FileMakaer Server will avoid the issue altogether if you can make that work.
Can you just use the layouts designed on the PC on your iPhone? Yes, but it won't be fast or easy due to all the pinch zooming and scrolling required. FileMaker 12 comes with tools to help design a second set of layouts for use with an iPhone and you may find this recent post over in the FM Go forum of interest: An Old Dog learns some new tricks...