16yrs old, first car advise?!

If this is a budget build, stick with the 318 for now. Start with rear end and gears then headers and exhaust. Stock long block 318 with headers 4bbl and comps xe262h cam is said to make 282 hp good enough for a start. At this point probably build the tranny to handle the next stage in power with stall and shift kit. Now you can't get much more out of the 318 cause of heads so next step would be EQ's or edelbrock. Now you got all the go fast parts now it's time for the bottom end either 318/340/360 or there stroker versions.