The course itself is around 900++. If you are taking the course in Selangor area, i think those dive center will have you learn the confined water training in their pool and also their MCQ exam. After that, go to island for open water diving. Personally, I would recommend you to take this because 4D3N is too short  . I took 4D3N course on the island and don ahve time to enjoy the island. Haha.

I'm not sure which dive center to recommend. Not from selangor area.    Ask those sifus here

Open Water Diver is the beginner stage of PADI diving course. After that it's Advance Open Water then Rescue then Divemaster.

It's best to get a good instructor that will teach you properly and not one that just wants to earn some money. There are many people who will recommend instructors and dive centers but first of all, do you want to do it on mainland or all on the island? I would suggest to do it on mainland first then go to island for certification dives but knowing lots of people, they prefer to do 4D3N one shot. I did 4D3N course last time but now I'll advice anyone who asks me to learn your theory stuff on mainland first and do some practical in swimming pool before going to the island, that way you'll have a more relax holiday and you can learn at your own pace.

Also it's monsoon season now, so most of the island resorts are close. You can of course get signed up for the course in Selangor and do your theory first then go to island when they open around Feb/Mar. Maybe you can provide your location so some of them here can refer you to their dive centers.

i took mine at SeaMonkey, PJ Palm sports.. same pool that global scuba uses.. and recently took my Advance with SiputScuba.. nice people.. awesome instructor. let me know if you want contacts

Klang eh. Long Adventure? Or Lee? Lee is my instructor and he's really good but yea he's in Klang.

Here's Siput facebook page, you can contact Nick or Lea Meng.
https://www.facebook.com/siputscuba?fref=ts

Have fun!