Well, if you start messing with metals other than Cu, Tin in small amounts, and Brass then galvanic corrosion becomes a
major problem particually with Al and Cu in the same loop.
As for bio growth, I initially was very, very fearful of it but haven't had any troubles with it.
Basically, tubing that does not noticeably admit light will prevent all most all bio growth.
UV light bad!
Combine that with a thorough cleaning of the internals of all parts before you assemble the loop and the use of clean distilled water should eliminate all possibilities of bio growth.
This is my experience so far.