You should see that both types of grapes are pressed off the skins.Since both make a white wine they should see limited skin contact time.Since your buying from a commercial grower ask them if they did do a short cold soak on the skins or not. A short cold soak can get more flavors and aromas out of the grapes. But as Wade pointed out before, if done too long bitterness from tannins can also get into the juice(too much of a good thing).
As far as yeast goes first time out use a good alround dependable fermentor that has neutral characteristics like ec-1118. That way you can see what the grapes give for flavors and aromas on their own. Next time you can then experiment with some other types of yeasts that can enhance the aroma and flavor too. A good source of yeasts can be bought and read about at more wines website. http://morewinemaking.com/search/103...eer/Wine_Yeast
For both the muscat and gewurz. you can look at using a yeast they recommend for terpene rich varietals.
The acid you should be using for all grape wine making is tartaric acid. It's the dominate type of acid in grapes. If an acid addition is needed that is the prefered type to use.