I would say Lugia (or shadow luigia) ,meganium, Celebi, magmortar Mew, and Groudoun
Nothing really; just some information for the unown report... and the pleasure you get!
with an action replay or some hack...
There are no legendary in dark cave in soulsilver that i know of, but i know alot of legendaries and I could list some of them if you want.
ditto and almost any Pokemon/mew and almost any Pokemon
To build a good Pokemon team, check the stats of your Pokemon. You do not always need well rounded Pokemon, since some stats can be sacrificed for others. Basically, choose what you think is good, and trial and error is your best choice. A great team can be made from any Pokemon (reasonably).
some trainier on the bike rute
yes. starters and some random ones
No. It will, however, bring some usually uncatchable old ones back.
Yes Raticate is not a half bad Pokemon but it has pretty bad defenses. It also has some bad special attack but it has some really good speed and ok attack PS: Furret and Tauros are both really good aswell!
You can find machop on some pokewalker routes, and in some patches of grass.
your mom will give you some and put on a Pokemon and trade from a gba or ds game.
You can get some plates from the SS. Aqua captain