He seems sort of 'distant' compared to how he is in the other movies; given Gisele's death, this is the reason. That explains his whole 'I have money, but all I really need is trust' speech to Sean. His need to keep people at arm's length (such as hanging out with a bunch of high-school kids) could fall under the same idea.
The way he's seen hanging out with models and making out with them shows that Han uses superficial relationships as a means of coping with Gisele's death. Seems horrible, but that is how some people fill the void.
Obviously, plot points from the other movies tie in with TD. Han giving up smoking explains his constant eating, as pointed out before. Having the money from Fast Five explains how he can afford a garage and can simply give away cars to people.
Remember, Han had stolen gas tankers, robbed $100,000,000 from a safe and helped stop an international mercernary criminal by taking down a MILITARY PLANE. With that in mind, DK was nothing compared to him as a criminal, which explains why he steals from him; not because he needs a bit of extra money, but because he can.
The question in my mind is was there to be a pairing between those two way before the fifth film. Gisele appeared in "Fast and Furious," but she didn't appear in that many scenes if I recall (I will need to see it again soon). Han only appeared in the opening sequences. Those two were not paired up until "Fast Five."
Yeah, he should have had a larger role in F4, F5 and F6 - those roles were mere a mere token of what the character could have been and it felt like they knew the fans wanted Han back but weren't willing to give up Dom/Brian's limelight.