You sound like you've given it a good start on life. The tree will probably grow in the limited light on your patio, but for the apples to produce and sweeten up, they'll need more hours of full sun. I'm growing a number of my apple trees in 15 gallon pots, in an area where they get morning and late afternoon sun, and shade mid day. The nice thing about pots is that you can move them around until you get the sun/shade balance right, then plant.
The website below is a good one for growing apples in a hot, southwestern, urban area. The book is very good as well. Good luck with your tree.

Here is a link that might be useful: Apple FAQs

Thank you so much for the info! I definitely plan to move the pot to a sunnier location once the tree starts to break dormancy. I will check out the site you recommended.