Depends on what you enjoy as far as atties go... many people say joye's are a solid product (not the best, but good). I personally enjoy HH .357's... but they are expensive. Good options are also Ikenvape (ikenvape.com) and Cisco (avidvaper.com) -- I would personally recommend those last two.
As far as
batteries go, AW IMR's are always a good choice. For 3.7V
vaping, go with the AW IMR 18650 (rtdvapor.com or supertmanufactoring.com -- have used both, and been impressed with both.) That is a bigger battery, but has great battery life. If you want the GGTS to look smaller, go with a smaller battery. Just depends on what you prefer. This is an example of something smaller than an 18650 -
AW IMR 18490 (18500) 3.7V 1100 mah
For 6V, you can grab 2x these batteries
AW LiFePO4 RCR 123
I really hope you enjoy your GGTS, and feel free to PM me.
BTW, I JUST noticed that you live in the phillipines so I'm sorry if this doesn't help!!!