Not only are you going to have a weedy mess from tilling, you will have a very bump, tear apart your lawn mower surface.

There is nothing you can do now to prevent the weeds. You did everything possible to get them off to an excellent start, and you cannot undue it. It is like pulling the trigger on a gun, once you fire, you cannot take the bullet back and will suffer the consequences of your actions.

Sorry.

If you've leveled it out and smoothed the surface, spray RU at least three days prior to the sod installation to kill off the new weed growth.

It will take 3 weeks but this will help a lot. Water it every day, 3x per day, to germinate all the weed seeds that will germinate this time of year. Do that for a week and you should have 80% of them sprouted. Then hit it with Roundup. Keep watering and hit it with Roundup one more time a week after the first.

Grading is not done with a rototiller. Grading is done with a box blade on the back of a tractor like this...

{{gwi:80981}}

Your rototilled soil will get bumpier and bumpier for the next 3 years until it is finally settled. You can level it then, but it is always preferable to not do the damage in the first place. It is a lot of work to do by hand.

Rototilling is usually only recommended by magazine writers. They are writers; not lawn experts. Real landscapers always use the tractor and only disturb the soil right at the surface.