1) you can registet your interest now on the ECDA website, you can choose up to 10 centres. Essentially this is a wait list. Whenever there is availability, the centre will call you up for sch visit. Other than Sparkletots, you can call up individulay schs for a sch visit before registering. You have to make payment to secure a place, but i guess you can indicate roughly when u'll start.
2) If by registration you meant on ECDA website, that does not serve as a formal registration. It's just an expression of interest. Some centres have long waitlist some are likely already available. You'd have to fill in forms and make initial paymemts at the school to secure a place.
3) not sure about subsidy for mothers who are finding a job, but there is an additional subsidy besides the usual working/non-working mother subsidy. Forgot what it's called but i think the centres will have you apply for that anyway and see whether it'll be approved.