We didn't spend silly money in the summer, comparatively. Our only first team signing was Mahrez for 60m, who has been very poor thus far and hasn't added anything we didn't already have (as well as hastening the departure of Diaz). We would've been far better served spending that 60m on cover for Fernandinho and cover for left back. As it is, we've again lost Mendy for most of the season and Fernandinho has missed a few games. At left back we've had Delph/Zinchenko to cover Mendy, neither of whom are left backs, and both of them have been guilty of giving away goals the past few games. In central midfield, we've primarily had Gundogan to cover Fernandinho, but he lacks the mobility to play the role, so we become a lot easier to play through. Generally I think we're a very well run club, but I think we planned poorly over the summer. There should've been another option on the table when Jorginho went to Chelsea, for example.
It's fair to say we've also been hit with injuries to other key players, notably KDB (he's started one league game), Silva. and Aguero. We've managed to carry these injuries pretty well in the circumstances due to the quality of the squad, but fair play to Liverpool they have been relentless so far.
And no, big questions won't be asked within City if we don't reach the semi-final/final of the CL. Clearly Guardiola is in a very comfortable position at the club, he's not going to get sacked if we don't reach the semi-final/final of the CL. The pressure for City to succeed in the CL always seems to be from opposition fans for some reason, it certainly doesn't come from City (though of course the club want to do well in the CL).