I need help buying subwoofers please?

Im turning 16 and i am thinking about getting some subs for my 1999 q45 infiniti. I dont know anything about them and i dont think i will spending anymore than 1,000. What size do you think i should get? How many do you think i should get? What brand should i get? How much does it cost to install? What are amps and what do they do for the subs? im willing to get an enclosed box and put them in my trunk, but will it take up to much space? Also im going to get a truck in 1 or 2 years, so will i be able to switch the subs over to my truck? Thankyou...and if you can only answer a couple of my questions then thats fine too.