Very much legal, never mind 'Dick' Roche. No keys if you don't have the €400 when closing, in fact this will probably be taken out of the mortgage cheque anyway.
Housing have common green areas and maintenance needs, similar to apartment blocks. Apartments have interior maintenance costs, refuse, and buildings insurance costs, whereas houses owners would be liable for these costs themselves.
As ClubMan says, the charge may vary, this will depend on the costs incurred by the management company (of which you will be a member).