Brewmaster is a top tier hero pick right now because of his lane tankyness, strong teamfight with ulti, and his ability to separate enemies.
You should rely on your ultimate to get kills on squishy heroes in the early game, and try to farm a blink dagger into aghanihms. This game I opted for some DPS items since Brewmaster has a crit and I was playing a sub game. Enjoy the sillyness!
Bristleback is a semi-carry tanky hero who can play a couple different roles, but is generally best as an offlane hero. If you're playing offlane, you'll want a few extra levels of his Bristleback skill to keep him survivable.
Slark is a strong agility carry who is good at snowballing because he's very survivable and has pretty good burst damage. Your point in combat is to be as annoying as possible and to harass your enemies with nukes and weave in and out of fight so that you can regen your hp and then come back in.
Witch Doctor is a super strong support in the current meta because his ultimate gives him huge tactical dps when the opponents are disabled! His stun can sometimes disable opponents for a very long time, and he's strong in laning in almost all matchups as well.
This game I played a hard 5 support hero and bought a lot of wards and detection. If you are the only support it's better to just sacrifice for the team and buy everything than it is to be greedy yourself.