Hey, I have recently purchased a 2000 Audi A4 Quattro 4-cyl... A few problems I don't know what to make of, can anyone help decipher these?

1. Whenever I come to a complete stop, or am just coasting and try to pick up speed again, whether I just put small pressure on the gas pedal, or slam it to the floor, for like the first 3-5 seconds it just kinda barely moves at like 5 mph, then picks up and takes off... I'm trying to clean out the fuel injection system with that cleaner u put in ur gas tank and we'll see if that helps, but other than that the only other thing I can think of is something like the air filter is old or air flow clogged, but I'm not a mechanic and I don't really see an easy way to get into the air filter box to change it... any thoughts?

2. Whenever I gear the car into reverse, it feels like the transmission drops out of my car and for the first 20 seconds or so, the brakes don't fully work, it's like I have to jam my foot down as hard as I can and even then it still doesn't stop fully, I have to flop it into neutral in order for the vacuum or something to kick in... I've had the brake vacuum line replaced and it doesn't seem to help???

3. The ABS is broken, but I'm not willing to spend like 1.4k on replacing it as it doesn't really need to be working right now during summer anyways... but because of this, the ABS light is on constantly, the Brake like is constantly flashing, which I understand... but the CEL is on too... would the ABS cause that to be on... I took it into a shop, and they had like a million error codes pop up, but they said none were really significant, but they didn't clear them or something, because the CEL is still on...??

Other than some minor problems, I'm loving the Audi and hopefully I can figure out how to do some of these repairs on my own since I'm not too happy on dropping thousands of dollars on a shop when I can do most myself, if you have any thoughts, please let me know