1) How do you get Dark Magician?

I can answer questions 1 and 3 for ya.

Dark Magician...I got a chance/offer to buy him when I got to area 4.

How do you buy him? You go to the Entrance Hall. I thought everyone knew that. It took me a while to figure out I could buy more monsters there.

Also you probably have a better chance at buying Dark Magician if your symbol is dark because I noticed that when I was dark I could buy him, Dark Magician Girl, and Summoned Skull...all good pieces btw.

Also, with Exodia, I, too, was confused on if they did anything, but I bought Exodia's Right Leg anyway, saying to myself, "I hope I get the rest of the Exodia pieces so I can summon Exodia".

I got Exodia's Right Arm from Grandpa when I beat him in area 1 and I bought Exodia's Left Arm when I got to either area 3 or 4. But enough of that...yes they do stuff.

The Right Leg, when attacking another piece, kicks the piece, and the Right Arm, when attacking another piece, swings it's chain at the piece.

Also, they're good pieces to get because they only require 35 MP and have like 240 health to start with. I think my Right Leg right now is a lv. 4 and has like 300 health.

For your second question what is the Best deck for the Beginning, I absolutely have no idea , but here's a clue : These are the first nine stage eneimies and their crystals:

Joey: Fire
Tristan: Wood
Duke : Dark
Tea: Water

Grandpa : ?

Weevil : Wood
Rex : Earth
Mai : Wind
Mokuba: Thunder

For your third question you need to get all 5 peices of Exodia and play all five of them and see what happens , because I do not know. My brother has three out of the five peices of Exodia.

You can buy all but the piece of exodia that you win from grandpa at the end of area one...all you need to do to get the body is to have the limbs in your hand ready for battle, then go to the shop and the body should be made available...then get all pieces to level 2 and with a fair amount of AP you can fuse the pieces to create Summoned Lord Exodia

Yes,If you fuse all 5 exodia parts,you will unlock summond Lord Exodia.And Whoever said that it didn't exist.....Your wrong.I used it against Kaiba.

There Really is no best deck because you pick which one your best with.

yea summond lord exodia at lvl 9 is the best creature EVER he killed a blue eyes ultimate dragon when i was at last arena in kibays place when the sun was out and the dragon was lvl 9 and i killed him in one shot hes the best

I belive that the water is the best to start with because you could beat joey easily then use free battle if you need practice

I think if your a beginer you should start with water in the first battle against joey you just use the attribute bonuses on the map and if you need to wait in the bottom left corner for him to attack your water monsters and the rest of your monsters could go through the ruins then attack his symbol and after you do that you could save and go to free battle mode on the title screen if you need to practice and get better at the game(free battle mode does not give your monsters any experianceor level them up)

Its probally best to make your own deck and chose water for joey,earth for tristian,cause you get fire guys from joey,light for duke, wind for tea and dark for grandpa.