B5 Audio wiring help

[EuroRizla]

Hi everyone,

 I own an A4 1998, I got her about 3 weeks ago and I'm pulling my hair out as I don't have Bluetooth or any decent speakers installed. 

 I would like to upgrade the headunit, door speakers, tweets, and shelf speakers. I will also add a sub in with this too. 

 Before I start this I would love some input on a few things;

1. I've got the speaker sizes down as 4.25" for the front, and 6.5" for the shelf, Is that correct? 

2. Can anyone drop a link to the correct 'Fascia' (I think that's what it's called), to fit an aftermarket head unit?

3. Best route to wire the battery to sub? 

4. Any tricks and experiences any of you have had would be nice to hear? 

 Thanks for accepting me into the club, and I hope I can contribute soon 🙂