I'm guessing at this but I reckon she could raise about 2-3 calves. She doesn't need grain but work on about 50 lb peak and then settling back to 25-30 lb later if she is fed well. She can get pretty much all she needs from grass, just as long as you provide enough of it.
Keep the ages of the calves within a few weeks otherwise the oldest may dominate the udder. You may have to get the cow in a bale or stall and put the calves on her for the first few days. The younger you buy the calves the better. And it is best to buy them all together and introduce them all at once otherwise she will have favourites. Once the calves know how to drink from her they will start feeding aggressively. Let her smell and lick them after feeding before you let her out of the stall. If this isnt working squirt her milk onto the calves and let her lick them. Sometimes it helps to keep them separate the first few days to make her want them as she gets a tight udder.
Jersey bulls will hit puberty early but I would generally wait till 12 months old before using a bull for breeding.
Hope this helps.