Can anyone please recommend a good car setup for me please.

I currently have a 1998 Ford Escort GTI with standard speakers. I
have a good MP3 Head Unit feeding them. I also have a mosfet 360w Amp
which I can use. I wish to spend around £250 - £300 upgrading the
speakers and installing a modest sub.

What would be the best route to go? I believe that I would be wise to
fit good speakers in the front doors, but I can only fit 10cm speakers
there.

Thanks in advance for any help.