1) If you do a search on the forum for "free stls" you can find some easy puzzle stl files to print. Or you can search on thingiverse.com
2) Small pieces take about 10-15 to print depending on the infill and speed you set it at
3) You can do multiples, but I would limit it too 2 hour prints just in case your print fails at some point.
4)It is a good DESK TOP PRINTER, simple mechanisms will work with .2 mm resolution, I would not do anything too complex
5) here is what I made on a makerbot replicator 2 which is very similar link!