loud is measured by decibels. airplanes dont have watts do they? but they are **** loud. you measure loudness by decibels. loud is completely subjective though. on any scale that is. 135 db can be louder than any one person could want, and then 145 is more like it for other people. 350 is quite the small budget to be honest. i would save up a while longer and drop some good cash on it. OR if you have never built/installed/seen a car audio setup in the works, go to walmart, get the cheapest shit that you can, and learn like that. build a couple sealed boxes for the sub, and build a couple ported for the same sub. theres no better equipment to learn on, period. once u get down your construction and installation skills, u can upgrade equipment and really have a nice system, looks and performance wise, and stand back and say "wow, this is awesome, i did it all myself"
you seem sorta young, (ur friends are just getting systems) how old are u exactly? if u have JUST gotten your license, you dont need bone rattling bass. if this is the case i advise you strongly to go the wal-mart route and learn the ground rules of a basic sub stage install. always run bigger wire than needed, as u never know what setup follows. I would buy a 4 gauge kit from your local audio shop. tell them you already have some subs a friend gave u and an amp, that you just need an amp kit. they wont bug u and pressure u into looking at higher end things this way.
4 gauge is good enough for most any single amp system, 1/0 gauge would be best though. learn the wiring diagrams and learn your car more importantly. build a box from 2x4's and cardboard to see the BIGGEST box you can fit, so you know this on later builds. knowing the biggest you can fit before building a big massive more expensive box helps, a ton.
thats really all the help i can give right now. other than a system in my honest opinion is 70% amp and 30 % subs when it comes to equipment. when it comes to install, its 80% install, and 20% equipment. you dont need the best in the world to get loud or sound good, if you know how to build a well constructed box, you really dont have to break the 5-600 dollar mark for a nice sub stage addition to your car.