I've downloaded iFruit for GTA V and I'm planning on getting the game soon. I don't have an Internet connection at my house. Since I've synced my iFruit, will I need to get online to play GTA V?
You don't need an internet connection to play GTA 5, but you do need it to play GTA Online.
Without an internet connection you won't be able to take advantage of the iFruit app, however. For instance: training Chop in iFruit will have no effect in GTA 5 unless you have an internet connection for both your console and your smartphone/tablet.