I have been to Malaysia and Pinang too. The best is to book a guided tour or rent a car and see hot spots of the island, like temples,beaches, musea, etc, etc. or buy a map and discover the gems of this beautiful island and Malaysia as well. Have a nice trip.
the best tip I can give is: rent a car or book a trip by Asia Travel (coach), they go to Cameron Highlands, book a hotel and see the Cameron Highlands, this area is much cooler than the rest of Malaysia. Visit a Tea House and drink a cup of tea from the Cameron Highlands Tea plantations. I did it.
I have never been to Rostov na Don but I should book a guided tour to learn more about the city because they know where to go and visit.
I have been to Bandar Seri Begawan and enjoyed it very much. Seeing interesting places and buildings as well as nature parks and the beach. The best is to book a trip to one of the major cities or to see rural Brunei.