Not really, no. There is a trainer that has Porygon 2 on Platinum, I forgot the area but I can tell you later. That is if you haven't met the collector.
you need to find 210 Pokemon to complete the pokedex
no you just need all the others
The national pokedex.
Obviously you need it to complete the national, otherwise darkrai will be missing:) not needed for regional though.
To evolve Porygon to Porygon2, you will need to have it hold an Upgrade and trade it. You can get Porygon-Z by having Porygon hold a Dubious Disk and trade it.
Porygon doesn't evolve at a level. You need a special item to make it evolve.
You do not need the national pokedex in platinum, simply talk to Bebe in Hearthome city
Yes.
To evolve Porygon in Pokemon Platinum you need to trade it while it is holding the Up-Grade item. This will evolve Porygon into Porygon2. If Porygon2 is traded while holding a Dubious Disc it will evolve into Porygon-Z.
NO you just have to get all the sinnoh Pokemon if its diamond or pearl but in platinum there is more...............
To catch Porygon in Pokemon Diamond you need the National Pokedex. After getting the National Pokedex go to Trophy Garden in Route 212 and talk to the owner. When he says he has seen a Porygon it will now appear in the Trophy Garden.
I think you need to trade it. But I don't no