3-5 days to process the acc? you just register for the acc? It should take about that duration.

If you deposit to the share acc from your MBB sav acc, it will take about 1 day (depending what time you deposit, they have different timing).

Cash account in my opinion is safer than margin for retail investor. If you have higher risk appetite, like most of my friends, they take margin acc.. limit is x2-3 of your amount in the trust acc.

Cash account... is like if you have 10k in the acc, your limit will be about 9.99k (the amount include the transact cost).