1) Nothing wrong with SCB, no minimum commissions is very cheap! You can queue your orders and let it fill over many days with no extra costs!!!
2) You dont have to create CDP acct first. You can open it with your DBSV acct.
3) Cash trading means place your buy order first and pay for it later within next 3 days via EPS for example. Cash upfront means you deposit your money into DBSV first and it will be subtracted from when you first place your buy order. So your buying limit is based on how much you deposit into DBSV which is done via DBS internet banking.
For cash trading, you need to submit your bank acct statement, CDP statement, pay slip, etc. for DBSV to give you a certain amt of buy and sell limit.
Cash upfront is only for buying, and selling within next 3 days. If you sell after next 3 days, it will be treated as normal cash sell.
4) There is no buy contra if I am not wrong. If you dont sell within next 3 days, it is not contra.
If you sell within next 3 days, then you can indicate the contra checkbox so that you need not pay for the buy order because DBSV will offset the buy and sell orders. You need to pay for the losses though if any.