Replacing brake lines on E53 is quite common. I bought this one:
https://a.co/d/ipp22rJ
and bought flaring tools, cutter, bending tool separately.
The real trick is to get it all bled when you are done. You will need to activate ABS pump bleed function with a scan tool.
Several others have replaced the rear subframe..Have a search.
Replacing all the bushings and other wear-out items makes sense while it is out.
If I had to do it I would buy a used rear subframe from a rust-free state.
Look at car-part.com.
I bougth a replacement FRONT subframe and haven't installed it yet.