At what Lead levels are respirators and hazmat suits required?
The magic words you want are "RRP", the EPA Renovation, Repair and Painting rules.  For a simple residential demolition that's all you need.  For details see http://www2.epa.gov/lead/renovation-repair-and-painting-program

Homeowners can take the RRP certification course (I did), but in most cases you'll want to ask the contractor for their RRP certification number, and ensure that the certified renovator is on site during the work. Every certified renovator is also a certified trainer, authorized to train and supervise the workers at a particular job site.

The level of lead in the paint does not matter at all under RRP rules.  And the hazard depends not on the level of lead, but rather the work practices used.  Sanding without a HEPA vacuum, for example, can put a huge amount of lead in the air even if the paint is relatively benign.

Note the gold standard for lead testing is not paint chip analysis, but rather XRF testing.  By investing in XRF testing you'll identify areas of the demolition that don't have lead at all, and thus don't need all that plastic, tape and other waste generated.