This is a really tough question to answer as the lifespan of your tanks and coils will greatly depend on how often you use them.
Generally a coil should last 2-4 weeks. It's lifespan will diminish greatly if you are constantly changing the e-juice that you are using with the coil. Coil life is also affected by the flavors added to your e-juice. Sweeter juices will reduce the lifespan of your coil as the sugar in e-juice will clog the coil with gunk faster.
A tank can last a long time if well cared for. Checkout our Tank Maintenance and Troubleshooting Tutorial for more info.