Before you use Imagers and stereo broadening tools, I would mix-everything exploit, which allows a lot of power and width.
A) Low bass voices in the middle. Then, for example, violins 1 pretty much left (panning) violins 2 pretty much to the right. Us so on until the whole stereo width is used nicely. You should also make sure that the important frequencies of rear instruments are not obscured by the same frequencies of front instruments. That does not mix flutes directly behind the violins. If you do that well you have already gained a lot of latitude and transparency.
B) Remember that you should keep your mix dynamic. Not all effects must always be set to 100%. To do this, you can use controller curves to decrease those things that are not that important and increase those that are important. This is true even for panning positions. If the horns in the middle should sound as powerful as possible, you can "shift" the violins aside even more during this time.
... as I said - keep everything dynamic.
If you have such a perfect mix, you can still use a stereo widener during the mastering process without any major correlation problems.
C) Attention: For many people, who mix with the goal "as wide as possible", the middle positions in the mix are completely missing in the end. Everything is on the left and right. Keep in mind that especially when the middle is occupied prominently, the left and right positions could be perceived even more intense.
For the evaluation of the width in the stereo field, I strongly recommend speakers.
Likewise, when pressing the mono button, the left and right instruments should not disappear.
D) A large stereo-wide and "Volle Karotte" can not be achieved with a piece of music that is completely "over arranged". Therefore keep the arrangement as simple as possible - according to the circumstances of course.
All the best
Beat