I'm not sure if I can be helpful here or not.
Reporting Services has built-in functionality to export to Excel format that a client can download, but the exported file will only contain content of the report that was converted. As far as I know, formulas and interactive features cannot be exported to excel from Reporting Services. You would need to link SSRS to your database and create a report that formats appropriately.
I am not sure if (I highly doubt) Reporting Services plays nicely with mobile browsers.
You could also not use Reporting Services and build up the excel files in your code logic. There are a number of open source libraries along with Microsoft libraries to handle Excel in C#. Here is a decent example from Microsoft:
http://support.microsoft.com/kb/302084[
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You can also find some nice third party ASP.NET controls that will render your data in a web browser and export to Excel. I have been happy with Telerik's UI tools, although you have to buy a license for it.
http://demos.telerik.com/aspnet-ajax/grid/examples/generalfeatures/exporting/defaultcs.aspx[
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You could also look into creating an ActiveX control that runs client-side and interfaces with excel directly on the client's machine through automation. (See the Microsoft example above for a start) Of course, all of your clients will need to use IE. I also don't know what sort of support mobile devices would have for such a solution.
Hopefully this at least provides you with a starting point for this project. Perhaps someone else has some better ideas and references, particularly for mobile applications.