Greetings ladies and gents,
This is my first post here. I've just acquired a '94 E320 Cabriolet in very good / excellent condition. It's a bit of a switch for me, I'm normally more inclined to the more low-brow, loud, greasy side of things - previous rides include a 2007 Triumph Speed Triple SE, 2007 Dodge Magnum, '62 Ford Galaxie 500 2 door hardtop, '62 Ford Falcon 2 door, 1979 Triumph TR7 convertible, etc, etc... the list goes on. Anyway, I am really enjoying this car, and plan on holding on to her for a while.

In my opinion (and from browsing the forums the last few days, I know there are some who'd disagree) the stock stereo, while intact and completely functional, sucks. Plus, I'm used to iPod connectivity. I'm going to replace the head unit, and at least some of the speakers right away.

I ran my VIN through the Russian site's decoder and got the following info, along with a lot more:

251
Becker Radio Mexico cassette, full stereo, electronic (с 01.04.1980 по 30.11.1990)

Becker Radio Grand Prix TR with remote control and automatic antenna (с 01.04.1964 по 31.05.1977)

radio MB-Exquisit - USA (с 01.07.1992)

814
Active bass loudspeaker system (с 01.10.1989)

Elimination of rear doors (с 01.11.1962 по 30.04.1974)

I've been doing quite a bit of reading here, and other places on The Internets. From what I can tell, this is a one piece radio, with an amp somewhere in the trunk (?). The dash speakers are ~5", and the doors and back seats are 5 1/4", with the doors being just a woofer. My understanding is that the amp takes an already-amplified signal, and then just powers the door woofers. Is this all correct?

I'd like to install an Alpine head unit (http://www.alpine-usa.com/US-en/products/product.php?model=iDA-X100) and upgrade the speakers, without an additional amp for now. I figure I'll add some Inifinitys or Alpines and see how it does, and then add an amp if necessary. So, here are my questions:

1. Can I just use an aftermarket adapter harness with the Alpine head unit, and access the current speaker wiring and amp that way?
2. Assuming that's the case, I could install new dash and rear seat speakers. I've read that some folks are putting 5.25"s in the dash with minor shaving - any specs available on depth, magnet width, etc that will fit in there? Additionally, how much depth and magnet width space is available back there? Anyone have any tips on speakers they've actually used in a Cab, and how they sounded?
3. A guy at a local (fairly respected) audio shop said that in these cars, they'll often leave the amp and woofers in the door, rather than running new wiring to those, since the speaker placement is kinda poor anyway, and the woofers will give some additional bass. Thoughts on this? Assuming the answer to 1 is yes, this would greatly simplify things. I can always add an amp and other speakers in there later on.
4. Again, assuming the answer to 1 is yes, will I lose any functionality, such as antenna up and down, amp switching, etc? And what's up with that speed switch business? I'm assuming the new head unit won't accommodate that, which is not necessarily a bad thing.
5. I checked out the W124 stereo article at http://www.peachparts.com/Wikka/W124Stereo. My understanding is that article is for earlier models... specifically, how does the head unit removal process differ from that article? Is it still necessary to yank the center shift console bits?

I realize this is a pretty substantial post for a FNG. Thanks in advance for any help, or links to help.