Ad 1: Well, details ... depends. If they're too small or not there, you don't have to map them. If they're unimportant to what you're trying to convey, you don't have to map them. If they're small locations, just use an icon like a triangle, asterisk or something similar - like in tourist maps where points of interest are indicated.

Ad 2: Symbols - this depends on scale and flavour. There's nothing wrong with drawings, just as there is nothing wrong with using simple icons (circles, squares, triangles) or just plain old dots. If the scale is very large, using just dots will convey that and leave the map uncluttered. You can always draw little cities to give flavour to the map, though to my mind it may be unnecessary.

Ad 3: Symmetry. Well, again, a matter of choice. The mountains are just abstract representations that say "here be uplands" while forests abstractly state "here be dense vegetation". I don't think they need rescaling, it's an aesthetic choice how large you want to depict them! For a sense of scale, a scale bar, a border or a graticule/grid would be a simpler solution than redrawing the mountains.

Ad 4: I don't think it looks like a map for 3 villages, to me it looks like quite a few large islands surrounded by shallow seas and straits.

Ad 5: Ok!