Hamas is getting a lot of international pressure behind the doors, and lots of threats forwarded to them. The truth is they don't want a war, most of the firing is done by other groups and limited to the Gaza vicinity towns. They could certainly increase firepower but they're uncertain of political situation at the moment. This falls on the politicians who did not plan well for this and giving mixed messages to military arms. If Israeli operation becomes official than they need to increase firepower.
Doubt it, there are heavier missiles but are not proven yet. The Iron Dome will be overwhelmed in Ashkelon and Sderot pretty soon so they should continue concentrating fire power to cause material damage and casualties. They can do this within a day or two once given the green light....