1. If I am not mistaken USD.  But let's wait for others to confirm.
2. See
FAQ
Once their customer base is large enough then they start charging.
3. I think normal US debit card is better. Combine that with moneymatch/instarem (if you have US bank acciunt)
4.Not sure.

1. Always pay in local currency. Let the CC convert.
2. No fees for Bigpay until further notice
3. More convenient if all your funds are from MYR
4. see above posts
Not recommended to open bank account unless needed. Some banks charge monthly fees if you do not maintain minimum balance.
Last I checked, some famous banks like WellsFargo or Chase need $1000 min or they charge you monthly fee $12. Some Credit Unions don't charge anything and you get a debit card. Some banks charge debit card fees. best to ask the people over there for options.

For cash withdrawal, few options
1. Use bigpay, pay Rm10 each withdrawal.
2. Open Citibank account in Malaysia. Citibank can do withdraw at any Citibank ATMs worldwide for free. But not sure about exchange rate.
3. You can survive without cash in US. Can buy $1 mineral water and pay with card at Walmart, nobody cares.

If you need to buy stuff from US sites that only accept US cards, you can go get those supermarket debit cards. Some charge fees for reload, so best to ask locals, or do your own research

kaiserreich
I will give you another different advise. Best to open a US bank account. Why?

1) you are unlikely to visit the US again. Why regret say 10 years down the road that you did not open account. Open 2 so you can keep the US account "active"
2) opening a US bank account open you up to cheap investment option in US as you are able to move money easily between brokerage
3) it's awlays good to have bank account overseas

There are so many US banks offering free bank account.

but USD800 is about RM3200!!

USD 800 or SGD 800?

In SG currently, withdrew from UOB atm with no extra charge.

As for exchange wise, slightly higher compared to xe.com, and after adding in the RM10 charge by BPM, the total conversion rate will be higher than those currency exchange in MV ady.

More expensive compared to change to SGD at a currency exchanger in midvalley. But I only withdrew 200SGD which was RM593.15 from BPM, XE rate was RM592.75, but after adding RM10 for the atm charge it was a total of RM603.15.

Based on kl remit exchange in MV, the rate was 2.965 so RM593. So I had to pay RM10 extra for the convenience. No idea why KL remit exchange's rate was the so good. This was all based on 14/7 rate.

For the RM10 fees from BP, I would say the withdrawal amount has to be higher to make it worth it.
On the other hand, even for the amount you mentioned, I would just use BP anyway, since it costs me time + money to travel to MV for exchange, not to mention the super long queue at changer.