Whether you need the resolution you have to find out yourself - what I can say is the 4k vid played back in fullHD is better than any fullHD content I've ever seen.
(However I am not so convinced by the real 4k capabilities of the Black - played back in native resolution I see noise and the sharpness could also be somewhat better)
Anyway, the silver and the basic hero are both decent cameras, check out some real-life tests, if you are satisfied with the result, buy the cam. The silver has the added
advantage of the LCD-screen.
As for depth rating: you'll be fine,
the stock housing can safely/officially go to 130'/40m, I don't know where that 115' figure came from... More important is
to always check the o-ring (unfortunately its a single one) and do a pre-dive check pushing all buttons in the rinse tank watching for bubbles. The housing
itself won't implode, only the buttons might become inoperable at greater depths.
Regarding budget: really depends what you want. For top quality video u need BIG LIGHTS. I mean, something in the 2x2000 lumens or more range if you want to bring
colors back. With these you already tripled the cost of even a hero 4 black... If you are fine with less, you can take filters (even a penny gel sheet does the job)
for shallow and use a single archon D32vr for dark places/night dives.
Best places to buy the Hero 4 Silver? If I'm amateur do I really need the 4 Black's higher resolution? It seems The 4 Silver would def do the trick. I'm assuming the housing that comes with it is secure enough? Saw that GoPro also makes a housing to go to 195'. I've been to 130' a few times. The stock one comes rated to 115'. How about the best, lightest one-handed mount with lights? I'd like an affordable set up if anyone has a good suggestion. Are all the mounts designed to use any GoPro?