You do need at least one FMPro 13 client to manage creating a new database or converting the fmp7 database and upload it to the server. I would advise Pro Advanced if you are only going to have one client copy. When using web technology depending on the number of users you may need a separate web server machine. Please see the recommendations from Filemaker.
Instant web publishing was retired in FMServer 12. FMServer 13 uses Custom Web Publishing and requires a little more knowledge of web languages. I wish IWP was still available for people who only need a way to access simple raw data on simple records.
You can also place the file in the default directory on the server and you do not need a client copy for that, but FMS13 will maybe not recognize the fmp7 extension for hosting. You will need a client to convert it. The trial version may do this for you, but I strongly suggest you buy one copy of Pro advanced anyway.