rear speakers + head unit

[da_houghsta]

im in australia and have the 2000 SB barina olympic edition (is the city model - base - with things like a/c, cd player, dual airbags, spoiler and alloys for free i think it was). so far ive just been using it as a run-around, but now would like to upgrade some parts.

1st is the rear speakers. i dont really wanna chop up any of the car, and after a heap of mucking around i finally got into the rear 1/4 panel on the inside to get to the speakser. i has some 4" sony xplodes laying around so i was going to fit them thinking they were the right size. turns out the stock ones are bigger, so what size are they and which speaker companies make that size?also the speaker wasnt mounted with screws either, was in a special mount that u put the speaker in and twist to lock it in place. then the mount was screwed to the body panel. would this mean there would be some vibration with this and should i screw it in as well? i also guess i could put my 4" speaker in there as well and screw it to the mount.

the other thing is that i want to upgrade the head unit. i have an older alpine cd player from a previous car - still works well as well, but i dont know how to go about installing it. ive done it before in other cars, but this barina has that heads up display thing (where the track number. clock etc are displayed on the top of the dash and not on the head unit) and i would like to keep that. is there any way that i could install the alpine cd player, and get it to display the stuff on the top part of the dash like the stock one did? i dont think its possible thoug as the stock one is obviously designed like it from the factory as there is no panel on it to display track info etc.

lastly, front speakers in the door. they are components i think as there is a tweeter near the door handle, so just wanna know the sizing for this.

thanks all