Salutations,fellow Singaporean.I first want to thank you for finding the Tek Syndicate community.
I'm like you,going to build a new system soon. But i am trying to avoid the local distributors as much as possible.Complete asshats,the whole lot of them. You can get all your components online and have them shipped over.Amazon is a great place.You can get free shipping to Singapore on certain components over there. Amazon does not ship over motherboards,fyi
You can try newegg for the components as well.Excellent prices but they do not ship internationally. Have you got Paypal? Paypal has this hopshopgo feature(partnered with comgateway).They can buy your goods for you and ship the over for a fee.By this method,you can buy pretty much anything(anything permissible by customs,that is).
The only issue with these options are that the local dimwit distributors is that you will not have local warranty support.You have to contact the vendor(asus,msi etc etc) directly and arrange for RMA/support with them. I'm willing to take that risk.I am flat out against the dimwits here.
With that being said,hold out for a week more.Black friday is coming and depending on your luck,you can save somemore on either builds above.Just don't look at microcenter deals.Doesn't apply to us.Items are in-store pickup only. Just stick with the major guns for us,amazon and newegg.
If you still want to buy local(nothing wrong with that),i suggest you look at these few stores at SLS.mynextcom,tradepac and pcthemes. These are the more "friendly" stores. The rest will confuse the fuck out of you and make you buy crap you don't want or need.I particularly like mynextcom.
As for your questions,
1.If your monitor has multiple inputs,then yes,you can connect both to them depending on the ports used.You can't display both console and PC on the same screen concurrently,if that's what you were asking.
2.Optical drives and HDDs are standard sizes.They'll fit in any case.Optical drives are 5.25 inches and HDDs can be either 2.5 or 3.5 inches.They both will fit in the HDD cages in the case.The cages are sized at 3.5 inches but you can still fix 2.5 drives with some screws(usually provoided by the case manufacturer.Just ensure you have enough SATA cables
3.That's your call on the additional fans.Just run with the original specs and components you have.Monitor the temps.If the temps are too high for your liking,then yes,you may install more fans.