Following video is not for a e89 z4 but it is very very similar to the e92 and its one of the most clear and easy to follow installs.
Jump to 9 minute mark for the front struts.
You probably don't have to remove the rotors or the fender liner as they do here but definitely the calipers.
The video doesn't have the EDC module but just follow the wiring to where you need to remove it.
Some decent written instructions here but unless you're familiar with it, may not make much sense.
https://z4-forum.com/forum/viewtopic.php?t=117994
You don't need to replace the springs but if you want to reuse them you'll need a spring compresser and electric impact wrench.
Overall, while it can be done individually, it'll help tremendously if you have someone assist you.
One tip, use a sharpie to mark the camber bolts on the lower control arms before moving so when you reinstall you can get the alignment back to what it was...somewhat.
You'll need an alignment afterwards regardless.
I think the adaptive suspension is closer to 900 each. I would recommend you check an indy shop that does a lot of BMWs and get another quote I'd think 2500 out the door would reasonable....it should only be like 250-400 in labor for the install and another 100-200 for alignment which is usually included.
Good luck.