Sorry to hear!
I have fixed a, 'clicky creak' like this by re-greasing the BB (Bottom Bracket) bearing and cleaning the area out. It is not uncommon that a BB starts to make noises. The give-aways are that it has jerkyness (bearings loose) and it doesn't happen at the same point of each crank rotation. Also that it happens on all 3 rings. The BB bearing should be rust & particle free, it should move freely without any okay. It should be well greased. Failing this, get a replacement BB bearing, you should be able to find the details on the existing one, make note of part number/width and diameter.
If it's not BB, it could be the peddle/s. A bent chainring. The previous owner upgraded the cassette to have more than 8 speeds, of which the front rings aren't designed for 9+ speed chains. It could be the tyre on the frame, the brakes and so on. It depends what you have done to isolate the noise. Sometimes we can be sure it's coming from one place, but then it turns out the sound/s is coming from somewhere totally different!
Re: 301/501.. I see little difference, both are 170mm crank arm lenth, fit square taper and are designed upto 8 speed. So both will work. The 501 I believe is a small amount more expensive and has a 4mm larger arm spacing. Anyway, you're still talking about bottom-end Shimano Tourney components so don't expect any notable riding difference.