The Clio performs really well on the track, due to its light mass and oversize brakes. I tend to do a maximum of 6-8 laps before heading back in. Just been using the standard discs + brakes and so far havent had problems with brake fade etc... Just make sure you do a cool down lap, minimal usage of the brakes.
Perhaps start the day with the traction control system on, as it doesnt engage too early and allows a bit of a play before it catches the car.
The overtaking policy would depend on the sort of track day. If it is not a championship round, then overtaking by more powerful cars will probably be limited to the straights - when a faster car is approaching, indicate (by hand signals) which side you would like them to overtake. Some track days Ive been to say that one should stay on the racing line and let the car get around you, others say to move out of the way. Best to ask the organisers on the day what the overtaking policy is. Also watch for flags, and keep an eye on the road ahead, sometimes if a person has an off they could drag gravel onto the track and if this is in a braking area, things could get ugly.
You wouldnt have to worry about 205GTis sporting track rubber, but more the high powered cars on the straights. The Clio can hold its own around the bends, with very few cars (besides the mid-engined and track specific beasts) being able to carry the same amount of corner speed. But on straights, it is best to keep an eye on what is behind you. Some cars can eat up the Clio with amazing pace, but only some