Hello thank you for the interest in our game!
1. Yes, we consider this a preorder for the full game not a purchase of the alpha state. If you purchase now you will have access to the full game and any post release content we offer for free.
2. Right now we have not optimized the game and we likely won't optimize it while we are developing the product. But I can without a doubt say that we aim to be playable on low powered machines.
Hope all that answers your questions!