Replace speakers on a SEL 5dr

I have a company car ( 5dr SE-L 75bhp) and plan to buy it off Skoda shortly. Am planning some changes to it and first is to upgrade the speakers in all 4 doors for something a bit better. Might also do the tweeters. Anyone been at it already. What is the beat plan? - rip our old and replace with a same fitting design or cut out a new hole for the new spakers to breathe better through its own mesh? Also re tweeter, suppose best is to surface mount it for better spread than to hide it behind current A-pillar panel. ANyone got any speakers to recommend and any pics?  I do not want to spend hundreds on this, something reasonable to improve the sound will do me fine.