Turning lanes, parking

1. You can add number of lanes as lanes=3 (or any other number). There has been a proposal on the wiki to map this, but I have never seen this on the map.
2. If it is used for parking tag it as amenity=parking
3. Adding detailed road features:
4. bus bays - I do not know. Maybe adding another lane for the part with bus bay?
5. parking - amenity=parking
6. pavements - see http://wiki.openstreetmap.org/wiki/Sidewalks
7. I do not know, but it should be.

Re pavements - the wiki sidewalk page was created relatively recently; also footway=both/left/right was already used (in fact, there are twice as many "footway=both" as "sidewalk=both" currently). If someone has mapped the fact that there's a pavement at the side of the road in the UK you'll tend to see e.g. footway= rather than sidewalk=; and I guess the opposite will be true across the Atlantic.

There are also people who suggest mapping them as a separate parallel way. This has been discussed at length on the tagging mailing list, and both sides of the argument think the other side is bonkers.

Personally, I'd say that while mapping sidewalks/pavements as separate ways might make sense in some places (such as here in Helsinki) where paths start off alongside roads but then often head off on their own, in most places in the UK footway=both/left/right/none or sidewalk=both/left/right/none is probably the better option (and it's less work to map)

As to whether you use e.g. "sidewalk=both" or "footway=both" I don't think that it really matters - it's one of the few places in OSM where a mass change of data for consistency (just "blah=both/left/right/none") wouldn't lose any subtle meaning. However, speaking as someone who occasionally walks home in the dark it's really useful data to have collected.