1. Can FM Go be setup such that it will always check for stock availability (online) to the FM Server and if stocks are available, confirmed, booked and print receipt?
--> If the server is available then yes, you can check data on the server. Or you can open the database directly on the server. A high speed (Lan) connection is best for this but can be done over WAN and 3G or 4G networks as well.
--> If the iPad is set up to print then the print command is available to the IOS device
--> All of this depends on the design and functionality built in to the database.
2. Does the FM Go store any data on the iOS devices? It will be good if the user can check for his confirmed order while offline
--> Complex question.
--- If the database is on the IOS device then all information is stored on the IOS device. If the database is being accessed from a FileMaker server then the data is being stored on the server.
--- There are ways to store the data both on the IOS device and the server and sync the new and changed data. Look at 360 Works mirror sync and Seedcodes GoZync products. Both are excellent.
3. FM Server can support upto 250 client, I suppose each FM Go is one client connection?
---> Yes but only when they are connected.
4. Based on the maximum 250 users, can we stick with one server setup or preferably to multi server setup?
---> The question is how many will be accessing the DB at any one time. It can get very complicated is you want multiple servers to serve the same file and then come up with a method of combining the data.
---> FMS can be split into a multi server setup where one server has the Databases, another the Web server.. See the installation manuals available in the FileMaker KB http://help.filemaker.com/app/answers/list
5. Is it recommended to go for enterprise DB such as MSSQL for the backend or stick to FM Server DB?
--> Not enough information available to answer this question. This depends on where the data is and how you want to access it. FileMaker can use ODBC and ESS to access other systems like Oracle, SQL server and MSSQL. Should you for this application... no idea. I need to know a lot more about your project.
FileMaker Server Advanced does not have the 250 user limit. There is no upper limit but performance will determine how many users can realistically connect to the server at one time.