Re: how 2 wipe cache partition s3
Clear the cache partition only once, and only if you have a problem related to cache files. Performance will not increase unless you have such a problem. It may actually slightly decrease performance due to rebuilding caches. Cache files are there to increase performance and best performance is normally achieve by leaving them alone to do their job.
Caches will slowly grow, often to 1-2GB depending on the device and apps installed. My Nexus 6 presently has 1.76GB. But they will max out and stop growing. at some point I usually never touch cache files for the life of a device.
You cannot increase RAM, it's a hardware limitation. You should not worry about RAM usage. Normal usage is around 70-85%.