The amount of grapes you will be able to harvest from your vineyard depends on the terroir and varietal. It is also dependant on how much fruit is dropped when thinning the vines during their growth cycle, as well as how many vines per acre.
You do not need an acre of land, to be able to make wine. You can plant a small section of 25 vines and have some fun, as well as purchase grapes. Often, amateur winemaking clubs or Co-Op Groups put together an order for grapes to be able to access quality grapes from a commercial grower.