well, the first thing I usually do when making balanced teams is picking a pokemon to centralize the team around. You have on, Breloom.
step 2 is about support. How are you going to aid Breloom in his sweep? How are you going to conquer typical walls that can take it's attacks with ease?
Let's start off by naming some walls- Gliscor, Skarmory, Celebi, Tornadus, Mew, Espeon, Xatu, Latias, Latios, Salamence- all of them pretty much wall Breloom, and can either OHKO it there on the spot or cripple it heavily and dispose of it later. If you notice, most of the counters are severely weak to Ice- Gliscor, Celebi, etc. So we will obviously need an Ice type, right? Skarmory, Mew, and Espeon are not weak to ice however, and often carry coverage moves that hit Ice types hard. So just slapping in an Ice type isn't a good idea. Make sure that it aids Breloom offensively, yet doesn't emphasize it's weaknesses. That is true synergy.