1. The H9 loads and runs only one effects algorithm at a time. However, some algos such as ModEchoVerb contain multiple effects, Spring reverb has tremolo, and different ET delay algos have extensive modulation, filtering, reverb, etc.
2. The H9, like the Factor stompboxes, works well in front of the amp or in fx loop depending upon your purpose and preference.
3. See 1. Multiple H9s are very useful for running simultaneous Looper, Modulation, Delay, Pitch Shift, and Reverb effects.