I strongly recommend using your oak and bourbon separately. That way you have more control over how much oak and bourbon character you have.
I've gotten good results from both chips and cubes. Cubes take a lot longer to reach their full potential. For a simple beer you'll age a long time, cubes are probably a better way to go. For a more complex beer, chips will provide you with plenty of oak character, but the complexity of the beer covers up the subtler flavors cubes bring, IMO.
I use oak chips on probably half the beers I make. I usually use 1.5oz / 3.3 gallons. So for a 5 gallon batch, 2oz is probably the most I'd go.