Hi and welcome to the Forum buddy!!!
Speaker size is not really of interest to me but if you type speaker size into the search bar up top, you will find the dimensions for sure
As for removing the door cards:
There is a screw behind the door opening mechanism and one in the pull handle/cubby too.
Once you have removed those two screws, you will need to prize the card from the bottom left hand side and give it a gentle tug towards you.
Be gentle or you will damage the card(s)/clips!!! Once you hear the clip detach, you can prize the rest which are all the way around the card.
Once they are all detached, lift the card upwards, but do remember to remove the window controller switches or the connecting plugs when doing so.
Get a Newbie post up when you have some free time on your hands and don't forget to post up pics too!!!
El