In the receiver chain like yours, the noise figure and gain /loss of each component contribute to SYSTEM noise figure and gain by the Friis' formula. It i good to know NF and gain/loss of each stage.If you need to measure the buffer parameters, you can do it. Measuring gain is easier than measuring NF. For NF test you need some gain after the tested amplifier to make the NF meter or power meter read reasonable values of noise power.
To the balun question, some 2.4 GHz amplifiers are designed as balanced stages. For such devices one can use baluns made of coaxial cable sections, or transformers also offered by Mini-Circuits.