How many hatcheries should i have?
You should have at least 2 hatcheries in you main base.When you expand you should have 1 hatchery per expansion and should be pumping out units like crazy.A zerg player should expand very early like when u get 2 hatchery then expand and pump out units.
Defences
Your defences should be creep colonies and hydras.Creep colonies are good for killing zerglings zelots marines and other units.Hydras kill air units and can go behind the creep colonies and kill them easier.In the begging you should get creep colonies and zerglings then get hatchery(2nd) then go for hydra by getting extractor (when hatchery or any other race is as close as to the extractor put only 3 drones or scvs or probes)and hydralisk den.
Killing Terran defences
To kill terran defences in the game u need hydras(at least 3 groups of 12)and queens.Upgrade hydras speed and range and upgrade broodlings(upgrade enshare also in case of wraths).Then get as close as u can and broodling all sege tanks and go in with all hydras.If u cant broodling then u need to get either tons of hydras to distract them of guradians and mutas(less money).Gurads get the land like bunkers and towers and make sure u have queens with enshare or overlords to get any wraths.In case of bc's plague them alot and use hydras to kill them.
Killing Protoss Defences
The protoss defences will be made of zelots,cannons,dragoons,sometimes reavers and templars(early in the game).You need hydras tons of them for zelots and dragoons.For templars Queens broodling and for reavers you need mutas.For the cannons the hydras will do.You must get the templars first before going in.Then get the reavers and send the mutas in and hydras at same time hydras distract the dragoons and zelots while your mutas go in and kill the reavers.