PB102 is also phosphor bronze. PB102's ISO code is CuSn5.
Rather similiar to the bronze used by Panerai for the Bronzo (CuSn8 or PB104-BS equivalent).
Difference is with the Tin content. More tin = stronger corrosion resistance. Also means higher prices since tin is expensive.
I would assume the biggest problem is with what's available in the market.
PB104 is harder to find; but of course with the right quantities, can be made.
Hell yeah.. it would give you a great patina too
i have some products made of PB102 that have been left out for years.
I'll snap a photo and show it to you. Just let me get rid of the dust.
As for the case back, its safer to use high grade stainless steel as terrenceterrence pointed out that we have a hot and humid weather.
The back would oxide faster and would not be pleasant to wear.
Test experiment: I'll put a piece of copper out, brush it with brine and water, and leave it aside. That'll help to decide if you want that touching your wrist

* my 2 cents. if i'm wrong, do help to correct me *