Controversial suggestion:
For fighting on level 4 GE, you need lot of things. Alcatraz, CDM, Zeus, COA, AO, Kraken and TA. If all these Great buildings are above 35+ level, you are in a strong position to fight on the level 4 GE.
For negotiation on level 4 GE,
@r21r answer is best regarding the goods. But needed more (750max) goods because without spending 10 or 20 diamonds, getting successful negotiate is very difficult. Have lost all my goods starting from 800 each in that age. With the friends tavern boost of GE with extra turn helps much on negotiating level 4 but it cannot stop losing goods. Luck should also favour much.