You can use current mirrors (simple or cascode if you have available headroom) for the various points you mention above.With current mirrors you fix the current in every branch and you also configure the voltage at the desired level.
Using ideal sources for biasing is not a realistic or practical technique since you can't evaluate your OTA's performance over corner (process,temperature,power supply variations) and mismatches (Monte Carlo simulations for this) and even for nominal state you don't have a fast way available to see how your design targets (gain,unity gain freq. etc) change with the variation of a current Ix at the x branch let's say.
As for Vbn Vbp Vcascn Vcascp Vbcm i already answered.