1. dont really understand motivation and driving factor for Venom to be evil in as mentioned in mg1 and same goes to real big boss. as in MGSV, felt more towards heroic.
i guess they didn't think metal gear series would go this far

2. is it mg1, venom tried to double cross real BB, thus real BB sent gray fox and eventually solid to counter him?
it was big boss that orchestrate the whole outer haven coup

3. Quiet who is working under XOF Skull sent to terminate Venom in early epilogue, and again in mission 11, but after recruit despite able to run away, what make make her change her mind to stick and be loyal to Venom (whom she assume real BB)?
venom did not kill her given the chance. deswai she felt venom could be her 'the one'

4. Ishamael is real BB, but he pee'ed in his pant out of tremble? haha
his not peeing la if you look closer you could see the IV liquid

5. read somewhere in NET, the idea to have decoy/doppelganger came from Zero who visited medic and real BB when they're in coma state in the hospital and real BB get a long with this idea. what puzzle me, they are enemies rite? the whole time real BB, Ocelot and Miller wanna take down Cipher/Patriot and Zero? 
its the whole rivalry friendly stuff between bigboss and zero. at the time zero is infected with parasite, his only hope for taking down XOF would be bigboss