iPads and iPhones use FM GO. Thus, some of these are questions are best asked in the FM GO forum.
2. that depends on what kind of access is available and how your users need to interact with the data. If you can link via WiFi to your network, accessing a hosted file will be a much faster process. It is possible to download data and then "synch" it back to a central copy of your database on a computer, but this requires setting up a system for this--there are two companies that offer products for this purpose: 360Works and SeedCode, and careful design and managment of your data.
3. That depends on what is hosting the database and how the client is accessing it. FileMaker Pro can host a databas file for up to 9 clients using FileMaker Pro or Go to access it. If IWP is enabled, up to 5 clients can use a web browser to access the database. Hosting with server supports a much larger number of clients than that.
Useful info about FMgo
There are some FMP basics in these links.
Now running FMPro 12 and FMServer 12. Have successfully uploaded 2961 records each with six images and a hyperlink.
Thanks for all your advise.