I had a similar problem a few years back and it was spark plugs. Make sure you get the correct ones otherwise you may still have issues!
NGK PFR6E-10 (3688) are the items to look for, e.g. http://www.roadtrackraceparts.com/ngk-spark-plugs-renaultsport-clio-172-182.html
I don't know the place but the price is not too far off. Take a look at Mick's prices (Diamond Motors) for an idea on costs from a reputable specialist.
https://diamondmotors.co.uk/timing-belts/
Sensible decision, mate. Feel free to hang around and ask questions. These are special little cars but maybe not for everyone. Take a look through the forum and Owners' Register to read more about these cars, things to look out for, etc.
@Rik Perry is an extremely busy man at the moment as his day job tends to get in the way.... hahahahaha! I'm not sure whether or not he's in a position to take on extra work as a result. I can certainly vouch for the quality of his work though. Top drawer.
I've never seen that type of crack either, mate. That looks like someone / thing has given it a whack.
Failed boot struts only typically break your skull as the boot 'closes' on you... :)
This (link below) should give you some idea of what a reputable specialist charges for cambelt, dephaser, etc. A main dealer will likely charge a fair few quid extra.
https://diamondmotors.co.uk/timing-belts/
If you're happy to move away from standard then I would highly recommend the PMS (Pure Motorsport) top mounts and strut package. It's not cheap but may be worth considering depending on your budget.
http://www.pure-motorsport.co.uk/front-strut-top-mounts-and-strut-brace.html