Although his surly attitude is unacceptable, there are contractual agreements that do prevent long haul crew from sharing bathrooms with over 30 passengers on some airlines for long flights. There is a specific reason for this but its very complex and if you do require further information I suggest you contact the airline in question as I dont work for AC so I can not really comment further for them.

Sometimes on the ground, it is safer not to have passengers embarking through an active galley. There may have been a spillage or something being cleaned up, or the crew may have arrived to the aircraft late for whatever reason and for the purpose of not showing anything frantic they have the embarking passengers avoid the galley area.

The 777 would normally have a First Class cabin for that single toilet, so in actual fact the standard is 2 toilets for J Class which you were supplied with.

Before you go on the defensive - remember I have not excused the Purser's poor attitude on this flight.