1) Steel bracelet,
2) Solid build, luxury feel, not too bling,
4) Can wear while doing sports, construction site visits, etc...
5) Prefer with date and day and GMT function,
6) Water Resistant to 100m, can be used for recreational diving,
7) RM20K budget.
Any recommend on the BRAND and MODEL NUMBER should be suffice, I will google the details from the web. Thanks. 
My friend,
That's too much to ask for a luxury watch. You'll end up with a "burger" on the wrist and a dial so busy that you can't read the time clearly

Day date model are usually ugly in my opinion but if you really need it then I guess is a must. Why would you need another GMT watch? Since you have the Rolex GMT TT.
All the dive worthy watch with GMT is anything but solid and luxury feel.
You can try this. Not for me but you might like it.
BALL Engineer Master II Diver Worldtime

Day date, Worldtimer (GMT on steroid!) and divable (300m so it can do 100m)
Sure cost less than 20k
Given in the same situation I would choose this
Seamaster Pro Chronograph Titanium

Tough and could be dressy at the same time. BTW you can even engage the chrono pusher while its underwater! Not available anymore but you can find it time and again in some used shop.
I love the pre Planet Ocean design. It's just my personal taste.
Regards
Tyler