1) it still will have the usual cash advance daily interest apply..
2) dont even think of it
3) just spend using your credit card like normal..

just consider it as a temporary credit limit increase of 25k until you use it up without needing to pay..
after u used up the 25k, ur cl will be back to 5k

and you got a very wrong perception, your card now is not -rm30k, i am not totally sure how it works, but i would consider it as 5k CL with advance payment of RM25k, i am not really sure you can spend more than 5k at 1 go..

It should be -25k in your credit card account but you can use up to 30k of credit limit.

If buying a house, you can use credit card to pay for 10% deposit right, eg: RM300k house, RM30k for 10% deposit is need

What I am curious is how you won RM25k? What campaign is it?

I am actually interested to know if you have tried to contact the bank to request for excess payment to be transferred to your deposit account. There is no harm trying.