Be careful with the oak cubes. I used 2oz of med roast French oak in a brown I made several months ago. I soaked the cubes for 7 days in bourbon, then poured the bourbon and cubes into the primary near the end of fermentation. Left the cubes there for 7 days in about 5.5 gallons.
The oak was overwhelming, IMHO. It's taken several months for it to start to mellow. Next time, I'd definitely still soak the cubes, but I'd use (a) 1oz (maybe less) instead of 2 and (b) probably only put them in for three days or so. A little goes a long way, and one of things I realized about the cubes is that the oak is powerful enough to drown out the malt. I didn't use smoked malt, and that might be something I'll do next time. But be sure you've got a strong malt backbone (if that's what you like) before adding the oak otherwise it's very, very easy to overpower everything.
The finished beer wasn't bad at all -- I'm still drinking it -- but it's definitely has a not-so-subtle oak flavor. It's "oak beer" in other words. Heavy, potent -- but not necessarily balanced due to the oak. OTOH, oak is a great flavor and has a bitterness that works nicely with the hops.