Maybank 2 card + OCBC ti would be a good start. You may read up on several prior posts for the benefit of both cards.

As for the electronic gadgets, you may look at Mach by Hong Leong which offers:
- 2% Cashback on Tech stuff including: Machines, IT Hypermarket, Epicenter and so much more (MCC 5045 and 5732) - capped at RM100(? unsure)
http://forum.lowyat.net/topic/242121

ps/ not to be busybody, but your estimated expenditure is that high? 

The first card to get is the OCBC Titanium MasterCard where you can earn 5% cash back for your Petrol everyday. This card also earns the cardholder 5% cash back for Dining, Telco and Groceries besides Utilities. For general transactions, this card earns you 1% cash back and the total cash back is capped at RM50/month. Therefore if you spend RM1000 on petrol, dining and telco, you would have hit the monthly cap and as such would not earn a sen further. However, if you do not have Credit History, don't be surprised if OCBC reject your application since are they are kind of "choosy" .

The other card to consider is the Maybankard 2 Cards where the AMEX earns you 5X Treats Points PLUS additional 5% cash back for any type of transactions on Saturdays and Sundays. Click here to read my review of Maybankard 2 Cards versus OCBC Titanium MasterCard.

The Maybankard 2 Cards AMEX is accepted at most merchants offering electronic gadgets i.e. Courts, Fotokem, Harvey Norman, Machines, Dell, Sony Centres, DiGi, Maxis, Celcom and even All IT.

And since you are new to credit card, I suggest you read my series of articles for Credit Cards for Beginners by clicking here to the prelude. After you completed this series of articles, you will understand why the Maybankard 2 Cards with 5X TP is the most rewarding card in the market currently for local transactions.

As for shopping , that's very general, you will need to go to each bank website and see if they offer any discount at your favorite outlets. For example, if you shop at GAP very frequent, Citibank credit cards are good.