The only way I can find to get bare feet is to choose Flip Flops and remove Feet from the blueprint. I’m finding all the same limitations with face editing as you mentioned. Many of the handles seem to be redundant and tend to have too large an influence. There are many realistic face shapes that aren’t possible currently. The shape of the ears, especially size is a big limitation…they simply morph into different shapes as you move them up and down.
As far as Maya source files, you can set up your download settings in Bridge: select your metahuman, click the gear at the bottom right of bridge, select Download Settings, Models, change the Metahumans dropdown to include Source Asset. The Maya scene will appear under a folder called asset_ue_source/MetaHumans/Name/SourceAssets.