I'm probably going to be helping to clean out a row home of someone who is a hoarder and heavy smoker.
Other than opening windows, what type of masks/respirators are recommended?
Any recommendations on air purifiers?
The home is a 3 story row home.
Open all window well in advance of cleaning out the townhouse - maybe even a day if you can. Keep the windows open if you can while doing the cleanout. Get some fans that will allow you to move air out of the area you are working - you will more than likely run across dust issues and other, more entomological issues - like mites, etc. Wear gloves while working - the latex dishwashing gloves are fine. Get a few pair as you want to throw them out with the other stuff when done.
If you are serious about air purifiers, look online - MSA is a manufacturer of safety equipment and Pine Environmental is a company that rents/sells safety equipment including personal protective equipment. They have charcoal that will trap the organics in the air - which you will probably run across - as well as dust, and perhaps non organic compounds. Don't go for the dust masks that Home Depot sells - they are for carpenters and tradesman and are for dust only.
If you are moving stuff up and down the stairs, pick up some booties as well, so you don't track things on your shoes. You may not have to wear fully protective suits, but Pine and/or MSA will have them.
As silly as it sounds - make sure you have a plan on how you are going to clean everything out, so you don't create more of a mess than is already there. Use Clorox and clean up after you clean out an area.
Everything you touch, wear, use - gets thrown out. Take it straight to the dump.
Leave the windows open after you clean out to help air out the building.
edit: Start at the top - possibly the attic, and work your way down. When you finish a room or floor, including all the Clorox, etc. clean up, leave the windows open and seal/block the area so you don't go back in. You don't want to track the stuff all over the place.
When the house is done, go back through and give it another clean, using milder soap and water. Don't close the windows or stop ventilation until everything has been removed, cleaned and cleaned again.
These are just my thoughts.