I am using AD9164 to synthesize frequency between 3 to 4GHz. I want flatness to be less than 1dB. The datasheet recommends 1:2 Balun from Marki as well as Minicircuits. Should I take care of anything else for matching apart from choosing the right Balun.
For the purpose of matching other than the balun you should consider the load, traces, and DAC's output impedance (including pullup inductors) at the frequency of use.