I split the major service job into 2 parts, as some people prefer to do the easy/minor service jobs such as filters/oil/plugs themselves.
I remove the engine personally, I just prefer the access with the engine out and not having to fiddle with the camshaft locking tools and cambelt tensioning/timing procedure in situ as it can take several tension/detension precedures to get the timing 100% spot on. It also makes doing the water pump/plugs/oil filter easier if required at the same time.
For the cambelt kit, water pump, aux belt, coolant, aircon regas, gearbox oil and PAS fluid i charge £850 inc vat. For the rest of the supporting service parts (oil, oil/air/pollen filters/plugs) I charge £150 +vat.
Clutch wise, it is a big cost and I personally would only use the renault part because they tend to have minor differences in torque ratings and if you buy from a factor there is every chance you'll just get stuck with a laguna v6 part. At £300 + for just the clutch kit and release bearing, if you dont have to do it then i wouldnt. However there is the whole 'whilst its out you might as well' angle as it would be a big cost to take the engine out at a later date to just change the clutch. But that would be a personal choice regarding what you think is good value.
As for the correct gearbox oil, its pretty essential. TRP is what you have to use, but renault normally only stock TRX and will fob you off with that, but it is not designed to work with the v6's synchros which are of a different material. However, TRP has now been superseeded and i have not tried the new TRS update so cannot comment. Obtaining TRP is hard enough as it is.