Welcome to the Forum
I have never seen a B7 in the flesh only read about them, from what I remember the engine uses modified twin scroll Turbo chargers so will not be cheap to repair/replace
I also thought the B7 was introduced in 2016 so not sure what model you actually have?
Then I would say your battery is dead the recent cold weather probably tipped it over the edge. New battery will probably sort it check that the battery is correct for the car and registered to ensure correct charging
There has to be something missing bent or out of kilter, Eibach are a well recognised make but there is always the chance that an odd length is in the kit.
I fitted a lowering kit to one of our Sons friends 3 series but he brought adjustable all round. Took a morning to fit then the following day after it had settled a couple of hours fiddling getting it sitting right (well how he wanted it)
That was about 2 years ago and he as far as I know is still happy