For HSSI Transceivers, you can tie Rx pins to ground by a big resistor (10K ohms). Do the same for PCLK pins. Tx pins you can leave floating. The reference resistor leave it as open circuit or floating. If you are not using HSSI, then you can connect HSSI powers to like supplies, just make sure the levels are fine and use power down option for HSSI (don't select altgxb channels in the design file). No need to use filtered or isolated power.