A) Yes it is, actually. Common aims for Alchemy were Chrysopoeia; the changing of less valuable metals into more valuable ones. (The traditional example being lead to gold.) Copper to platinum definitely qualifies here. The DC for a platinum piece is a 10 (Typical Item) or 15 (High-Quality Item) dependent on how the DM feels about currency. Seen here:
http://www.d20srd.org/srd/skills/craft.htm
B) Correct, and in this instance it would qualify as a transmutation...meaning it would be copying Polymorph Any Object.