$0, that would be excellent! In order to find out near what the payments will be, you have to do a separate entry with only your income again. Hopefully, it will make sense for you in terms of taxes. $80k+ is a pretty decent amount to be forgiven.
Yes, for 2019 it would be easiest to just stick with the higher payments unless there is a pay period where he gets a lower paycheck. You could recertify early in that case (using paystubs). But if you decide to file separately, I would definitely do taxes ASAP in 2020 and recertify early.
You were correct earlier. You can't be on the standard plan having consolidated. But making the same payments on a IDR plan will be the same thing. As far a buying a house, you might want to check out some of the threads here. Some government loans will actually take into account your lower payment instead. That's how a lot of people with IDR plans are able to buy houses with significant student loan debt. On the other hand, that's a long time to wait for loan forgiveness.
Hope you find a plan that works best for you. If you have any more questions, ask away. Good luck.