Not an owner yet but planning on owning one either by leasing or paying it off.

A little background on myself is that i've been wanting a '98 a4 (for its looks) for a long time, but now that 2 newer models have been released, i'm leaning towards the more updated models. Looking forward to owning an a4 '05 body and i have some questions that maybe you owners have unbias answers to. I've been reading a little bit on this forum and finally decided to make an account here to get a better understanding of this car mostly hoping to gain information that i would not have taken into account for before buying one.

-Any changes between the '05 models within its generation? (not sure if i worded that right )
-Is there any model version of '05 a4 that is not worth buying?
-What happens if i use lower grade gas?
-Should i lease or do monthly on the car? (for those who have an opinion on it)
-What is a good dealership to go to for this car?
-Heard euro cars are high maintenance and even this forum agrees, but i also read that it's nothing that US and JAP cars don't have issues to. So i'm wondering, is there ANY unique issues that a4's might have that other cars usually shouldn't have?
-What is an above-average deal for this model that i should be going for? I researched online and the a4 '05s were going for around 30k with 50k+ miles on it

My previous ride was a van that i didn't care much for so excuse me for asking any unoriginal questions.