skeeter

How do i know when my cassette is worn out ??
What's the best kind of lube to use on my chain??
What kind of mileage should i get from chain & gears ?

ridelugs

prolink is the best lube readily availible. its thin, penetrates well, and gets nasty shards of metal outta yer chain. apply liberally, then run your chain thru a rag, then apply more, and wipe off excess. your cassette is shot when it starts to skip under load, ie the rear mech is adjusted properly but when you stand up and apply pressure, the chain skips. you can get 5000 miles from a well maintained chain and cassette, if you continually flush with prolink, after every muddy rainy or dusty ride, or every 4 rides or so if such conditions do not persist.

waterrockets 

You need to spend some quality time at https://www.sheldonbrown.com

San Rensho 

In a (n opiniated) nutshell.

Measure chain often for stretch/wear. Replace it well before the limit. If you replace it before the wear limit, the cassette will last a very long time, years depending on use. You will know the cassette is worn when you put a new chain on and some gears start to skip.

Wipe the chain after every ride. Taking it off and cleaning in solvent is a waste of time for normal use. Lube your chain very SPARINGLY with ANYTHING. Motor oil is as good as any proprietary lube.