If you upgrade to modern 9 or 10 speed freehub you can still use your friction shifters (bar end or DT) and derailleurs if they spread wide enough, but you will have to use a narrow chain which will get dropped between chain rings of older cranks.

To go modern you need at the very least, cassete (and wheel to mount it to), 9/10 chain, crank for 9/10 speed, and appropriate bottom bracket for the crank.