Hello, I am new here but I have a lot of experience in Clio. So before I introduce myself I will answer to your questions.
First of all speakers, on the parcel shelf, will deliver you more sound boost but you will have a lot of quality loss so its a good decision not to add those
I have tested a lot different setups in Clio and I found out that the car itself has very good speaker positions and depth so that you get the topmost sound with a set of good speakers. The factory fitted speakers sucks, exept those fitted in MTV edition Clios where they are kinda better.
So, if you want a quality upgrade I will suggest my current setup. 2 Set of Focal Access speakers, one coaxial for the back and one divided set for front. The divided set comes with tweeter and crossover.
You can look at these: Focal Access 130 A1 and Focal Access 130 CA1. Both 5" models fitting renault clio. They have maximum power of 100W wich is enough for the factory HeadUnit, and also for a small power amp on later upgrade, BUT besides their low wattage they are extremely reliable and powerfull speakers, with a little help from renault's speaker position. If you want even more power you can look on other focal models wich I also have used and I am fully satisfied with them.
Also, for the woofer, you can keep your current woofer and amp as they should be loud enough to fill your car with bass.
As for the shop, since I suggest you should do the speaker upgrade yourself (if you can) as its not very difficult