Hydrogen and methane, when produced via water electrolysis with the usage of electricity from renewable energy sources (RES), could be used to help decarbonize sectors of the economy where other alternatives are either unfeasible to apply, or more expensive. Given Greece's favorable potential with respect to RES, such as wind and solar power, said power-to-gas (PtG) renewable products are considered crucial in the country's effort to meet its national environmental and energy policy targets. Meanwhile, they are also in accordance with the country's commitment to the EU's broader 2030 and 2050 climate and energy targets in plans such as the Green Deal. The present study proposes several key scenarios involving variants of PtG investments for the case of the Greek energy system, examining the coupling potential with both the natural gas and electricity transmission systems. The analysis emphasizes on setting up the basis for realistic mathematical simulations and their latter accurate techno-economic investigation and optimization, while indicative key performance indicators are identified towards the consistent evaluation and benchmarking of the different investments in question.