You should have no problems with the 9.5 / 10.5 wheels with those tire sizes, again just depends on offset
As to the staggered tires on all 9in wheels, I would say it may not be ideal with what you would want. The fit of 275s on 9in is borderline...maybe someone has them. I am not so familiar with the fit of 18s and potential for the tire to rub on inside...with that offset, unlikely to rub on the fender either way.
Even if the 245 & 275 on 9in wheels fit "ok", the look may not be so desirable...stretched look on the front and fat look on the rear. If sticking with 9in wheels all around, consider doing a smaller uptick in staggered tires...could get away with 235-F & 255-R or 245-F 265-R while using same width ratio, but probably most here would rec just sticking with same tires all around.
Lots of posts with pics here on the site with various options wheel and tire sizes...pay attention to what effect and look you want to help finalize your choice. Hope that helps some....
Yeah, if the plan is to run same width wheels all around, I would stick with same size tires all around. This will allow you to rotate tires. You can also run spacers in the rear or select a lower offset for your rear wheels to flush out and fill the space in the rear fenders. At the end of the day it comes down to what goal you're trying to achieve with this setup.