Hi @LevelUpOrNot. Regarding your second point about which probe(s) to use for a given gene, this question was just addressed in another post. Regarding averaging values across a certain tissue, you can do this for three resolutions by setting the “Resolution” tab at the bottom of the heatmap:
This will average probe expression across all samples for a given structure. If you want to do anything more complicated, I would suggested downloading the data.