There'll be plenty of business for those who get in early as keyholders/cleaners etc. Do a good job and you'll keep the client.
Plenty of recommended keyholders on various threads throughout this board and they'll all be damned busy over the next few months.
As to legality etc then i wouldn't have a clue who is and who isn't registered or what paperwork shoved in front of me would prove otherwise as it'll be in Spanish, as for comeback if something goes wrong or not done/delivered as promised then what exactly do you do to enforce anything in Spain. ''50€ community charge v 125€ community charge, 2 pools in J5, resident only Foro ?''
Living predominantly in the UK i took a chance buying in Spain, I took a chance with my Spanish Bank, my fittings, all my electrical goods, my lawyer, my agent (they were all legal as well, cashback ?? !!) my keyholder etc.............. it's still all a bit of a chance but so far it's working.
Word of mouth works well for me, and if it then don't work out then change to another word of mouth recommendation, bit like everyone's favourite pubs and restaurants