I’m not going to answer all your questions, but I’ll try to explain what I think is best.
While designing fonts, it is usually smart to keep composite glyphs, unless they are just a way to get a start for a final result. Most composites can remain a composite, some examples are agrave, aacute, acircumflex, ograve, ntilde. Other glyphs are too complex but can get a good start through complete composites. They require some fine-tuning. For example the Bitcoin Symbol.
In general composites which end up with overlapping contours require attention (manually adjustments).
While it is perfectly normal to design your glyph outlines without taking care of the horizontal position, most font designers will ensure the final font only contain glyph outlines where the left side bearing point is set at x=0.
Usually marks (non spacing / combining diacritical) will have a negative LSB and a AW which is zero.
Do inspect fonts like Garava and Bahnschrift to see how other font designers have set these values.
Hope this helps.