I am travelling to Australia (Adelaide) on PR (E-Visa) 1st time from India (So do i need any transit visa at Hong Kong & at Perth airport if i stay inside the airport only & my time b/n the connecting flights is less than 8 hrs)
As David Richerby stated in his comment, you don't need a transit visa for Perth if you've already got a visa for Australia.
And according to Timatic, you don't need a visa for Hong Kong either if you stay in the transit area:
TWOV (Transit Without Visa):
Passengers with a confirmed onward (Air-to-Air or Air-to-Sea) ticket to a third country within 48 hours. They must stay in the international transit area and have documents required for the next destination.