What kind of ventilation do I need in my workshop?
If you are doing a lot of soldering then a dedicated soldering fume extraction unit would be a good idea. You can put the end of the hose right next to the soldering operation.

For an example on YouTube of someone who does a lot of soldering using one and showing how much gunk they stop you from breathing:

Loius Rossman: A word on soldering and fume extraction