Viharas were for the purpose of living, Chaityas were assemblies for the purpose of discussions. Further, Chaityas were with Stupas, Viharas did not have stupas.
The Ikshavakus arose on the ruins of Satavahana power in eastern part of the peninsula in India. The Ikshavakus left behind many monuments at Nagarjunkonda and Dharanikota. They were a local tribe.