No, Spanish law allows you to maintain dual nationality, although the regulations of each country will have to be taken into account.
Birth certificate: 6 months
You must present the renewed and old passports before a notary.
Instruction 29 / September / 2015 DGRN On application of Law 12/2015. I.4.3 1.a) "The Certificate issued by the President of the Permanent Commission of the Federation of Jewish Communities of Spain has special probative value ..."
Those over 14 years of age have to come and sign together with their parents or one of the parents with a notarized and apostilled power of attorney from the other. Children under 14 should not travel to sign, their two parents will do so or one of them with a notarized and apostilled power of attorney representing the other party.
The deadline is September 30, 2020 although as a result of the state of Alarm for COVID19 it is likely that this period will be extended.
No, only if you live or work in Spain.
Obtaining Spanish nationality by this means is configured as a right so, in the case of having signed with the FCJE certificate, having passed the CCSE exam, lacking a criminal record and providing the rest of the necessary documentation if the notary attests that everything is correct, it will be granted.