Can one take small luggage bag with them to sky deck ??

Yes..Your bag will be scanned just like in Airport..

Yes you can, they have a scanner and metal detectors for backpacks for example

I dont see why not. There is a security checkpoint the same as they have at airports with the walk through scanner as well as the x ray conveyor belt for bags and purses. Just don't stuff it full of drugs, firearms, and weapons and you should be fine :)

Yes

You can take your suitcase with you, but they will check it in the security area before entering.