OP-
Acceptance rates:
Tufts 14.6%
UM - for OOS college of engineering - 11%
CMU - 17%
NE - 19.3%
BU - 22%
Safeties need to be schools that you are guaranteed admission, that are affordable, and that you would be happy to attend.
The danger of overshooting your list is not having any acceptances come the spring.