It depends upon the complexity of the install -- placement, obstacles to work around, etc. Get advice and quotes from 2-3 electricians who can see your environment. I'm going to offer a rough, round $1,000-$1,500 for the complete install including HPWC but that's without knowing a lot of variables.
As for the Powerwall install, there are several different approaches you can use. I'm not familiar enough with the various inverters that will work with it, but that is one way to do it.
As far as setting both cars to charge at different times, some inspectors will allow it, and others won't. Your electrician will help you with the permit/inspection process and perhaps clear it ahead of time with the inspector - and for the work you're doing most locations in the US will require permit/inspection. If the window for charging both is that tight, they may not allow you to do that.
Good luck!
As for the Powerwall install, there are several different approaches you can use. I'm not familiar enough with the various inverters that will work with it, but that is one way to do it.
As far as setting both cars to charge at different times, some inspectors will allow it, and others won't. Your electrician will help you with the permit/inspection process and perhaps clear it ahead of time with the inspector - and for the work you're doing most locations in the US will require permit/inspection. If the window for charging both is that tight, they may not allow you to do that.
Good luck!