dewd, PM me anytime with questions, i love helping people out with SQ.
wanna a know a trick for a really kick-ass install?
ok here goes:
for the kickpanels, look, i have no idea at how handy you are with working with your hands and fabricating things, so i'll just try and explain anyway:
To make some kick ass kickpanels:
1) remove factory kickpanels
2) get what we call masking tape, i think its called GAFFER TAPE in the uk
3) now paste this tape everywhere, you'll wanna paste it inside the cavity behind the kickpanel and over the wires etc, basically you'll paste this tape everywhere where the plastic kickpanel USED to be, except the tape will cover the "cavity" aswell. make sure you use 2 or 3 layers of it
also make sure you cover half of the area where your floormat is.
you then smear petroleum jelly thickly allover the tape. this can be found(the petroleum jelly) at any chemist or healthstore, this will be a relase agent for the fibreglass, and it is really cheap. you'll need about 3 tubs of the stuff,
i usually buy these from like 3 different stores or else the shopkeeper might think im gay or something 
 
you then cut little pieces of fibreglass, little pieces measuring roughtly 5cm x 10cm will do, you gently place these over the petroleum jelly.. you'll kinda find that they'll stick to it... 
you then mix up some fibreglass resin, around 500ml for each side,
you then apply this resin over the fibreglass...
what now happens is the following:
The fibreglass "sets/cures" this now forms the solid backing for your kickpanel.
just watch out the amount of fibreglass you use, fibreglas can get VERY HOT when curing, dont want to set anything on fire or anything.
now you cut 2 speaker rings for each side, one 5.25inch ring, this is basically a speaker mounting ring made out of wood, the inner will be about 5" the outer part of the ring about 5.9"inch
you do the same for the tweeter.
you then need the following:
8mm wood drill bit & drill
8mm wooden dowel rod
you then drill 2 x 8mm holes anywhere in this ring, you then cut various lengths of dowel rods, for e30 purposes thay will vary between 4 & 8cm more or less..
whats going to happen now is you are going to place these dowel rods thru the holes you just drilled in your speaker ring, you are then going to angle this ring in the right position, you then use a hot melt glue gun to glue the dowels to the fibreglass backing you made.. this ring is obviously where your speaker isgoing to mount into.
what u need to do aim this ring, for optimal soundstage the best "target" position would be like 5cm above the centre air-vent. aim the tweeter along the same path. the opposite speakers must obviously fire in the same position. you might not have enough room to angle  the speakers completely due to too things,
one, the globebox needs room to open, and 2) your accelerator needs about 1inch clearance between ur kickpanel and your pedal.
not too worry.. good quality speakers like scanspeak etc normally have good off axis response, this means you dont really have to be right inline/line of sight of em to get the best of them when listening.
I've dont some tests, i've installed my kef coda 7 woofers and tweets in factory locations, for the tweeters i cut a hole in each plastic kick panel and mounted em in. the imaging is quite good, i'd say just a tad higher than dash level. the midbass response lacks due to the "metal" being the enclosure and not perfectly sealed either.
but the bmw e30 seems to image well. i'd say that designing and building good kickpanels will provide a soundstage around 6inches below the rear-view mirror. this is considered very good in sound quality terms.
and will score high in the imaging/soundstaging department at any iasca competition.
my pickup scored 46 out of a possible 50 for imaging!
the only problem i forsee with the bmw e30 is that the enclosure "volume" in litres, i dont think it'd be possible to do more than 3litres each. this is less than optimal, so bass response/midbass will be less than optimal, but a well tuned sound quality subwoofer can help mask this.
1 x single high quality 10inch in the rear, fire-ing directly thru the rear parcel shelf and perhaps angled slightly to the front is all that'll be required bass wise. ohyeah, the metal in the vehicle will definitely have to be dampened slightly to get rid of the "tinny" sound, that metal ringing sound you hear when example slamming one of your doors shut. this is the metal "echo-ing" if i could put it that way.. some sound deadening in the right places will sort this out. not much work compared to some vehicle as the e30 seems to generally be quite a solid vehicle, 
remember, you could remove your ski hatch, or cut holes in your rear shelf for the sound to literally leak through, but this isnt optimal and will lead to what they call time-alignment errors. the sub-bass will not blend into the audio properly, there will be a slight delay. 
since ive only had my e30 a few weeks i havent dont my install yet. will do so when the pickup is done. busy spray painting it. but basically you want the cone fire-ing towards the dash, and ideally simply an acoustically transparent mesh to protect the woofer.
The only way i figure this is possible is to basically cut an 11 - 12" hole in the centre of the rear shelf, then to build a 0.9 - 1.0cu'ft enclosure which bolts under-neath the parcel shelf, the subwoofer will then fire directly thru this hole and into the cabin, one should seal between the subwoofer box and the parcel shelf somehow. you dont want the sub-bass leaking into the boot, the enclosure must ultimately be one with the rear shelf.
The enclosure MUST be air-tight, and as "sound-proof" as possible, thick 22mm mdf should do the trick.
At the end of all this, if the boot of the vehicle was wide open it should make too much of a difference in the sound.
a wooden "frame" can be made to go onto the rear-shelf of the vehicle. this frame can then be covered with acoustic cloth.. this would HIDE the subwoofer, but at the same time let the sound through.
i think the e30 will sound very good if the above guidelines are used.
ohyes, when installign your amplifier, make sure your fuse is WITHIN 18 inches of the battery.
Also, try and run a GROUND cable from the front of the vehicle to the back and connect this to the same ground point as the amplifier. your SOURCE UNIT will perform better when given its own dedicated/shared ground with the amplifier. this is much better than factory head unit loom ground. much over much-ness i suppose. but at the end of the day it all counts..
this is how (by paying attention to details) i managed to score 350.5 points for sq at the finals last year. i might add that the setup in my vehicle was the cheapest and the most basic out of all the installs.
i've been competing since year 2000. so you can PM me anytime with questions as how to start competing..
its very easy to get into it... and LOADS of fun once you compete. you get to meet lotsa fellow competitors and learn lotsa tricks etc...
the above was just a rough crash course. hope there is some useful info there
Cheers
Anton