Line Item Dimention Vs Hig Cardinality

HI ALL

           I have a problem with a cube and the below are the challenges...

                   1) can we use High cardinality / line item dimension if we already used one of these(High cardinality / line item dimension)?

                   2) while loading 4lakh records in to cube, i tried optimizing the cube by segregating characteristics into different dimension and i am successful in bringing down the percentage levels but all dimension levels are almost near to 30%. I Have only 1 key figure , will it cause any problem....

         please let me know the concept....

Thanks

vijay