1. Many of these satellites are cubesats. They hitch rides as secondary payloads on launches, and in batches. In Planet's case, they've launched many batches, some as large as 20-48 satellites.
2. Not really. Kessler syndrome is the general name for this phenomenon, but it's not a huge concern in LEO. In LEO, there is enough atmospheric drag to naturally deorbit spacecraft. For US based companies, regulations mandate that they have a deorbit plan within 25 years. For most cubesats, their orbits are low enough that they'll naturally deorbit within 5-7 years.
3. Most people generally think that any hazard in LEO will not be caused by launching more objects, but by having objects collide (or having some weaponry intentionally explode objects) causing debris that is spread more widely and too small to track. Currently JSpOC in the US tracks most objects the size of a baseball or larger in LEO and coordinates with various commercial and private entities to put into place plans for collision avoidance where possible.
2. Not really. Kessler syndrome is the general name for this phenomenon, but it's not a huge concern in LEO. In LEO, there is enough atmospheric drag to naturally deorbit spacecraft. For US based companies, regulations mandate that they have a deorbit plan within 25 years. For most cubesats, their orbits are low enough that they'll naturally deorbit within 5-7 years.
3. Most people generally think that any hazard in LEO will not be caused by launching more objects, but by having objects collide (or having some weaponry intentionally explode objects) causing debris that is spread more widely and too small to track. Currently JSpOC in the US tracks most objects the size of a baseball or larger in LEO and coordinates with various commercial and private entities to put into place plans for collision avoidance where possible.