May i disagree with previous posts as to choosing contactors and mcbs, first establish what make of mcb you are using then get a copy of their distribution boards catalogue (with technical advice in the back normally) if it lacks technical advice then ring them with type and wattage and no' lights per circuit, you will find what size and type of mcb and contactors you need for any given type and no' of lights in table form, if you do it by guess work or pick next rating /size up you will only set yourself up for premature failure of contactors and nuisance tripping, contactors should be rated for the switching of high inductive loads specifically inductive lighting , just buying any main stream contactor will again only lead to problems, all this must be worked out before hand as it may need 16amp mcb's and 2.5mm wiring to compensate for inrush , Square D books have an excellent section at back to help you identify the correct mcb for given job and associated contactors you will need and as mentioned before the spacing needed between contactors is also calculated for you.
Designing this type of supply needs to be done ahead so you dont fall foul of nuisance tripping and not been able to upgrade mcb due to cable size to small, ive followed many rule of thumb companies and explained to customers why their lighting trips or their contactors only last a year or two, finding the correct mcb and contactors using the correct research will supprise you just how far out you can be if just doing a load calc to work it out, also different brands can have different tolerances and thus results may differ.
Also as mentioned by other post feed you contactor load channels via mcb's then have seperate mcb fed control circuit via switches to energise contactors, no overload protection required on contactors as your mcb's already do this.