On top of Stefan's previous good advice, I would add that you need to provide the strongest light you possibly can indoors. You cannot provide too much light to this plant if it will be a house plant. Right in front of your sunniest unobstructed southerly facing window would be ideal (assuming you're in the northern hemisphere).
The taller these plants get indoors, the more likely they are to suffer complications from insufficient light. A 7 footer would be near the ceiling here and the top of it would basically never see the sun, which will pretty inevitably lead to stretching (taller, weaker growth). Bottom line is that these Euphorbias are awesome container plants until they get too big, at which time you kind of have to restart them from cuttings if you want them to continue to be happy (and fit) in your home. On the plus side, it's ridiculously easy to start one from a cutting, and I can give instructions on that if you like.