I'm not sure if stacking can be completely disabled, however why are the photos stacked in the first place? You will be asked if you want to stack when exporting for an external editor and 'stacking' of JPEG and RAW files can be disabled in the preferences. What more ways are there, that photos could get stacked, where you do not actively do it?

Concerning the second point: If you have one folder that contains all photos (also in sub-directories) you can simply select this folder, or even the entire drive, to see all indexed photos that are on it. If there are several folders/drives you can select multiple ones, using CTRL. A more elegant solution might be the creation of a Smart collection with a filter, that simply applies to all photos, e.g. Star rating between 0 and 5.

*Edit: I cannot verify right now, but apparently stacking does not apply when within a collection (see here). Therefore using one big collection might actually solve both problems