Based on 747 eng ground run knowledge/experience.
1/ If running an outboard engine above 1.3 epr (RB211) then opposite engine must be run up to 1.3 epr to balance. So if testing no1, move thrust levers for 1 and 4 upto 1.3 epr then carry on with no1 to required setting leaving no 4 at 1.3 epr.
Inboard engines no balance required.
2/ The 'flags' test you are referring to was on a JT9, which had 2.5 bleed vavles, these were located on the core behind the reversers and opened/closed at a certain power setting and starting, the JT9 has whats called 'RABS' reverse air bleed system, and opened/closed the same bleed valves, so having the reverser deployed would not help at all.
You can't do the 'flags' test as mentioned above on a RB211-524 as the bleed valves are on the core under cowls however you could check for the opening and closing of them by monitoring the egt, there would be a increase or decrease of 40-60C when the valves opened/closed.
These bleed valves are for engine air control, eng bleed offtakes for services are different, HP/IP, these can be monitored through the CMC on 744, or valve position lights on the classics.
Hope that helps.