Off board and connec problem

hi i got 2 problem
i got cube black with px4 frimware
first problem:

  1. i connect to telem 1 silk telem - b.rate 5700
  2. connect to telem 2 r_pi b.rate 5700

when i connect the pixhwak also to the computer i cant data from him

secend problem
i try to connect optical flow to my pixhwak - i dont understand if the optical flow is enogh to make me use the offboard mode ?