Found a solution for the soft throttle:
Went to Autozone and picked up a pack of generic throttle return springs and a cheap APC throttle return spring bracket. I bent the bracket flat in a vice and it works quite well. There was an unused threaded M4 hole in the cable pulley that I used for the other anchor of the spring. The pedal could still be a little stiffer but it's a lot better than before. Of all the springs this was the stiffest one that could fit between the pulley and the cable guide arm. I'll probably make a little extension piece to add to the APC bracket or make a new bracket altogether so I can run another spring on the other side of the pulley for some more tension.