/App_Data and /Data need to be fully writable by the web process user (the user that is the identity on the application pool).
I have never heard good news from people using 1and1 shared hosting but their dedicated servers are a good value. 1and1 always seems slow to update ASP.NET in shared hosting, until recently they only offered 2.0 ASP.NET and I'm not sure if they now have .NET 3.5 or .NET 3.5 SP1, mojoPortal needs at least .NET 3.5 SP1
If it does work out well for you at 1and1 please do let us know, I like to collect such information so I can know what to recommend or recommend against, in the past I always told people to not use 1and1 shared hosting because they only had 2.0 .NET. But I have not heard much since they started offering 3.5 .NET so it would be good to hear about it good or bad.