turtwig (the grass/ground starter) piplup (the water/steel starter) chimchar (the fire/fighting starter) (the part of ground,steel,and fighting part will be learned while leveling up and evolving)
no because you can die
sorry but you have to get another diamond/pearl/platinum game and trade the other starters from there.
No. The starters are still : piplup, chimchar and turtwig.
No, but if you catch all the sinnoh pokemon; Prof. Rowan will offer you one of the three Johto starters.
No. You can only get 1
Breed a female starter
you trade using the global trading station (GTS) or trade with someone that you know that has one
There isn't a second set of starters.
Obtain 200 Pokemon in Pokemon ruby, sapphire or emerald, then go to professor birch and you get to choose one of the johto starters, then you migrate the starter you chose to Pokemon, diamond, pearl, or platinum.
The only way to get the Sinnoh starters in Pokemon HG/SS is to trade it from games Diamond, Pearl, and Platinum.
Some Pokemon are able to walk in amiti square, but in platinum even starters and there evolved forms can walk with you.
All the starters are equally good.