I'm so new, I don't even know what the difference between a sewing machine and an overlocker is... could someone please tell me!

Hi! I've been thinking of getting a machine of some sort that er... sews. My resolution for this year (and life, hopefully!) is to use and/or upcycle pretty much everything that is sitting in cupboards or gathering dust. My first project is going to be to make cushion covers from our old tshirts. My second is going to be to make some of Jacko's clothes from our old tshirts, my third is going to be making shopping bags from...yup, you guessed it ... we have a lot of old tshirts!!

So my questions are:
1. How addictive will this new hobby of mine be?
2. How quickly should I expect the addiction to take hold?
3. What am I buying?
4. Where is the best place to buy second-hand? (that you know of)
5. Is it pretty easy to teach yourself how to sew?

Thanks in advance!!!