1: Those don’t stack, but with the new patch the Mineral scanner is 45%. The game should use the value of the best facility but it may believe the Robotoid is 90 % (30 + 30 + 30). Need to test this to know for sure
2: Only way I know is to use individual ships with don’t get hurt order (using Don’t get hurt as fleet order don’t work as it will always break formation and ships will follow their own orders). A minesweeper will do fine. I sometimes build a comboship with minesweepers and loads of PDC rto take out fighters for blockading.
3: No
4: No, there are no differences in the bonuses for MB and PPB. IIRC the Meson bLaster has shorter range though so if you use the default “Optimal” strategy, you will be closer when firing (getting 10 % extra to hit for each square).