A. Never ever query RS Database directly until you know what are you doing. The queries could acquires lock which could affect overall performance of RS.
B. To know about report execution stats, you can use ExecutionLog view in RS 2008 onwards or following query with NOLOCK Hint.
Select CAST(C.Name AS VARCHAR(20)) [Name],
E.ReportID,
E.InstanceName,
E.UserName,
E.RequestType,
E.Format,
E.Parameters,
E.TimeStart,
E.TimeEnd,
E.TimeDataRetrieval,
E.TimeProcessing,
E.TimeRendering,
E.Source,
E.Status,
E.ByteCount,
E.[RowCount]
from executionlog E WITH (NOLOCK) inner join catalog C WITH (NOLOCK)
on E.ReportID = C.ItemID
C. RS exposes almost all the functionality via SOAP APIs. For example this sample published my MS shows how to get security information on Report Items http://msftrsprodsamples.codeplex.com/wikipage?title=SS2008R2%21RSPermissions%20Sample%20Application&referringTitle=Home
To know more about RS SOAP APIs please see http://msdn.microsoft.com/en-us/library/ms154052.aspx