Moving to Madid.... (Madrid)

Hola a todos....

I am moving to Madrid, from London, in 2 weeks...(lucky me), My company will put me up in an apartment for a couple of months, but I have a few questions that maybe some kind souls can help me with..!!

I know Madrid is a big city, but if i was to attempt to find a flat along the metro line 8, between central and Campo de las naciones, is this an expensive tube line..?? what kind of prices for a decent sized apartment can I expect to find, to rent per month..??

do most apartments come furnished or non furnished, or is it usual to find both..??

are there certain areas I need to avoid..??

OK, thanks to anyone who replies, now that the move is fast approaching, I find more and more questions each day..!!

b