I?ll belatedly answer this myself, now that I have the experience.
1) Yes. Absolutely, and in fact we applied immediately.
2) No financial documents were required. See below for my summary of the process we followed.
3) I haven?t tried this yet however the word is that my non-EU spouse holding Spanish residency cannot enter the UK without a visa. One could either apply for a paid tourist visa or, once resident in Spain and exercising treaty rights, one could apply for a short-stay EEA Family Permit to enter the UK. Search for Surinder Singh if you want to learn more about why this can also apply to British national and their non-EU family members.
I recommend you head down to the place where you will apply for residency - get the form, the checklist of requirements and also find out about appointments. Once we had our dossier, we just took our chances without one and they gave us a slot for later that very morning. I have read that appointments are a bit more scarce and can maybe take weeks to obtain - much will depend on where and when you apply.
Along with the appropriate forms, passports, photos etc. we needed:
a) Proof of marriage. It might depend on where you were married but I was advised to use an attestation from the main British Embassy in the country in which we were married, and this was translated into Spanish by a State-approved translator in Spain. In our case, our original marriage act was not required by the Spanish authorities - just the British attestation to our marriage & an official Spanish translation of that document.
b) My Spanish registration as a EU national - this took an hour including the trip to pay ?10 at the bank.
c) Our proof of lodging (as in both of you) - this is an inscription in the locality and applied for at the town hall. In our case, as invited guests, a form was filled out by the owner of the house and supplied with a copy of their national ID card. The resulting document took a week to be prepared.
The application for residency was done in person, took 20-30 minutes and we were given a letter with a code so progress could be tracked online.
I think it took a month or two to see an approval however the date to go to and process the resident?s card with the police was another couple of months later. That process itself was very quick and involved fingerprinting and a signature, I think. Yet another month wait was estimated before we could collect the card - I called up a week before that month was up and learned that the card had already just arrived (so about 3wks). Joy! Everything was completed in around 5 months - from arriving in Spain with our proof of marriage to resident’s card in hand. I understand one is allowed to reside and work from the moment the application is entered (not waiting until the card is processed months later) and the date on the card, and the European Law, seems to suggest this is true - the 5yr card expires 5yrs after the month during which the initial application was lodged.