hi! im fairly new too, and i have recently bought a reprap machine from bitsfrombytes.com, unassembled(because its more fun that way!) so check that out! to answer ur questions...
no gasses given off...too small a scale to cause harm, and the plastic doesnt burn, only heated up until more managable to squeeze through the extruder.
it can handle a massive amount of accuracy in terms of detail, but how much detail were you looking to produce? the rapman 3 from bitsfrombytes.com has been used to build tiny figures and small scale buildings for the surrounding areas of train models railway tracks, so as you can imagine that is SMALL!
in terms of getting a smooth finish, you can quite easily sand and smooth the plastic, and still benefit from an impressively stong stucture.
and yes, you can build parts that lock into each other, the best thing is with this machine is that you can pause the extruder/g-code process, wich will allow you insert electrical components into the build if you want! that sealed the deal for me as my first project is going to be an intergrated i-pod docking station!
hope i have helped at all!!
cheers russ
