Hi Snights - and thanks for stopping in and sharing with us.
No reason what-so-ever that it can't work !
As Ciel pointed out - you are kind of off to the right start by by keeping it all open & honest and talking it through. That's key.
And although right now it looks to be largely sexual driven - which is fine - I would only advise that you start some talking right now about what it would mean if one of the FWB connections actually started to deepen. Because that possibility is definitely there. Better to talk about & plan for that now then have it slap you in back of the head later and lead to all sorts of drama etc.
As far as the "equal treatment" etc, please keep in mind that loving relationships are not some type of competition. It's about caring deeply and trying to find the right balance that meets everyone's needs & desires. It's nothing about "equality" at all ! There's lots of things to be 'balanced' - time, space, emotions etc. Some compromise is often involved. But a big part of the definition of love is having a sincere, deep desire for the happiness & fulfillment of those you love.
It's work ! No free rides here
Depending on which directions your sexual desires lie in regards to gender you will likely find partners that are quite comfortable in the role you wish them to play - as you say - secondary. Likely that many men will be quite comfortable in that role as it meets their desires too.
So absolutely it is workable and not unrealistic at all. But it takes complete transparency and good communication skills. And knowledge of all the various twist & turns that can appear.
Good luck - learn, love & don't HURRY !