Agreed, preheating will not be easy to implement, but based on the reprap community experience, as well as the powder printing threads on the reprap forums and this report it seems to be a necessary evil to prevent the plastic from curling as it cools.
Not really worried about the aesthetics. Just want a reliable, usable, low cost material that can be sourced relatively easily.
Haven't tried them myself yet, but from what I've seen on the net, and what is readily available for sale on various sites (including ebay) 100um doesn't seem hard to achieve.
What do you mean?