There are many ways you get one after beating Red, you get another one in the fertilizer shop and you get three keyitems in fisherman houses but ther are still many more ways.
go on bag then keyitems then click on item finder
No, you can't get all of the Legendaries in Pokémon HeartGold although you could trade all of the Legendaries in.
I put a link to a guide all about legendary pokemon in HeartGold in the related links.
You catch them all....
no
Yes.
Pokemon HeartGold can communicate with all the DS Pokemon games. :c)
you throw pokeballs at them
migrate and trade
I think you can get all of them....
cant unless you migerated
In the top of the battle tower