I've added a link that you can find a walkthrough from.
www.psypoke.com and it tells you everything where it get Pokemon about shiny Pokemon everything check out more then just the walkthrough
To find it go to spear pillar and you will battle the commanders and in the distortion world at the end is where you find Giritina! I'm not sure about the item though and a good walkthrough website is http://www.psypokes.com/platinum/walkthrough.php
route 218 (good rod)
You cannot find Bulbasaur in Pokemon Platinum. you can only get a Bulbasaur through trading from Pokemon Leaf Green or Fire Red. You can even use an AR to get Bulbasaur in Pokemon Platinum. Sorry I don't remember the code. Have fun and good luck.
you can find a octilery at route 233 with a good rod
use good rod at route 222
Route 226 with good rod
Canalave City use good rod.
There is not a complete walk threw online, but you can get extremely good books from gamestop or walmart.
use a good rod in Route 223 and theres a 5% chance you will find one
to me no
head down of solaceon town and see if you can find a firsherman. talk to him and he will give you a good rod