Congrats!
Where to begin. There. Is. So. Much! Assuming you’re going on an official re-visit day, your tour will take you up to North Campus where much of the CoE stuff is. If not an official re-visit day, after your tour make sure to take the bus up there (free) to really get the full experience of what that’s like. For context we have twins at UMich. One in CoE and lives up in North Campus. The other in LSA Honors in South Quad which is very central on the main campus. They both love where they are, though DS on North Campus does sometimes go back and forth >1 time in a day which he does not love; 1x/day he’s fine with.
Definitely spend time walking around downtown (off the NW corner of the main campus). Casual eats? Frita Batidos is always good. Something a little nicer? You could try Peridot. Late night drink - hit The Last Word (trust me please on this). But as you can see in this screenshot from Maps, downtown is stuffed to the gills with places. You can see the corner of campus in the lower right of the photo.
If your tour should somehow skip the law quad and library, visit those for sure. Beautiful.
Nice day, feeling energetic? Walk over to the Arb for a stroll.
Zingermans is a total institution if you want fantastic deli.
While I’m spending your money, if you can swing it stay at the Bell Tower or the Inn At The Union, both right on campus. Otherwise downtown at the Residence Inn by Marriott downtown. Then +/- 2mi away there are all sorts of places to stay with lower rates as needed.
Let me know if you want any other type of info 
ETA: check this thread too