1. front L and front R SEPARATE! adjust spacing, adjust toe-in, future changes.
2. center channel, tricky, you want the speaker as close to the monitor as possible, I find just below the monitor best, dialog will be anchored to the image.
a. You could build a center channel recess in the front/top of the cabinet, then raise the monitor up to finish just above it, i.e. the speaker does not move. The face of the Monitor would be 'behind' the face of the center speaker which needs to be considered. Cloth panel, put speaker in from behind.
b. Center Speaker goes up/dn with the Monitor.
I don't like rear ports, thus I chose this Klipsch center with front ports
they make a wireless version
klipsch has some refurbished, you can find them for less on eBay etc ....