So the layout would be:
SWM LNB --- 21v Power Inserter --- 4 port SWM splitter --- 2 port SWM splitter --- Broadband DECA ---ethernert and power supply for DECA unit.
All other ports on the SWM splitters would be connected to receivers. Does it matter which port the 2 port splitter and the DECA unit connect to?
Some of the installers here strongly recommend NOT putting the power Inserter before the splitter. They actually recommend that you put it on it's own dedicated output from the splitter. The reasoning behind this is that if for any reason, the power inserter gets disconnected and reconnected by someone who doesn't know what they are doing (spouse, kid, cleaning lady, etc...), there is a 50% chance that it will reconnected backwards which would cause you to fry all of your receivers in one fell swoop. If you put it on it's on dedicated leg out of the splitter, that can't happen.