what cards in the set are starter exclusive and only contain one in the starter?

Those with Starter rarity on the card list.

are they all one of?

are they all one of?

For the most part yes. The only doubles I recall you get is 2 power of the dark side on Kylo's deck and 2 awakenings in Rey's deck. Each deck comes with 1 lightsaber, 1 aim, 1 use the force, 1 close quarters. I might have missed some.

I wish that they would have made Finn as a rare card in the game like the FO Stormtrooper. I built a Poe + Finn deck for my son, but I couldn't fit elite Poe (1 point too expensive), so I had to go with elite Finn. I don't want to buy another starter deck, so I am currently letting him proxy the other dice with a normal six sided. Of course, this won't work if he wants to use it in more than a casual game.

The really good cards you get when you buy a 2nd starter are:

Mind Probe from the Kylo Ren starter

Force Throw from the Rey Starter

2nd Finn die from Rey Starter

and to a lesser extent, an extar 1st order Stormtrooper from the Kylo Ren Starter... in case you have very few characters that stormie can be helpful.

Singles market is cheaper than a second of each starter if you only want those specific cards. The second of each starter is better value for money if you can make jse of the other cards. Ie I'm considering a second of each starter to leave as separate decks for playing at home or teaching. That way I do t have to rebuild decks to do so and can just switch out those few cards and dice.