yes we can create cube from multiple iqd's , we have to 
first import the primary datasource which contains most of 
the structural data item required for the cube creation, 
and then other sources,by inserting the data source 
separately.
Good practises:
1. we can incrementally update the cube.
2.check the cube status periodically
3.run the test cube with a small amount of data.eg., if you 
have 1000 records , we can assign 300 records from each 
data source and perform a sample test cube.
4.we can do partition, to improve the runtime performance.

yes we can create a cube with multiple IDQ's as data 
sources,for this insert data source of tyye Impromptu Query 
Definition in Transformer model.
afer creating a cube u can---
1)Partition a cube 
2)Update a selected cube by batch file or by macro  
3)Apply security to a cube
4)Compress a cube.
5)Publish that cube on Upfront.
6)Use that cube as DataSource  in  FM in Cognos Series 8