The H9 will only run one effects algorithm at a time, although a few algorithms such as the ModEchoVerb combine multiple effects like chorus, delay and reverb; Spring Reverb includes tremolo, etc. An H9 could replace any one of the delay, chorus, flanger,  phaser, or reverb pedals. It depends how many effects you want to use at once. I would plan on using the H9 to replace the delay and reverb pedals, maybe keeping your Phase 90 or Flanger if they have distinctive EVH effects you really like. Two H9s could replace all delays, reverb and chorus, and keep just the Phase 90 or flanger.