<p>With hot plastic being laid down layer after layer, I am worried about fumes. Should I only print in a well ventilated work space? Should I add additional ventilation?</p>

There are some contradicting sources out there on whether plastics, especially ABS, have toxic fumes. It is well known that PLA is food safe, as it is an organic, biodegradable polymer being based on a particular cornstarch. This means that PLA
is
safe when printing, although it can produce foul smells from the dyes and other ingredients. As for the other plastics, it is most commonly said that the fumes are toxic, although, as stated earlier, there are some contradicting topics on this.
Here
and
here
are some articles for further reading.