Sentinel,
1. No need to inform bank in advance. Just tt the money to your account. Once the amount arrived, you need to fill a Form R (if I am not mistaken) and the bank will help you to submit to bank Negara.
2. You will be in the lime light lol but honestly I don't have the answer for that.
3. Apparently, its not mentioned in IRB web. I doubt the normal officer would have the answer for you.
But one thing for sure, Malaysia is yet to have a double taxation agrement with Brunei. Further details, click on this link.
http://www.hasil.org.my/english/eng_NO2_3.asp#kandungan