If you want the silencer asthetic, thats your call, but as I said, I Highly recommend you play with it a couple times before you start adding stuff.
For me, short barrels are worth their weight in gold, I love the mobility/pointability it gives me.
Leave the gearbox stock until it breaks. I wouldn't even open it. Unless you really know what yours doing, you will do more harm then good by opening it.
If you have a couple bucks to throw at it, I would buy a hop-up rubber, an SCS, maybe a couple mags, and then save for a better rifle.
Not matter how many parts your put into it, a kracken is still a kracken. By the time you replace enough components to make it comparable with a high-end rifle, you would be better off just buying a CA or G&P
It's better to light a candle, than to curse the darkness