Although not Spain, I have been through a similar process with Italy. I am Australian by birth and Italian by descent and I applied for Italian citizenship only recently.

My meeting at the consulate was to check the forms, make sure I met the requirements and of course to take the cash application fee.

I didn't engage an immigration lawyer, but in another instance I did and it was worth every cent. I would suggest at least an initial meeting is a good idea.

There are no tax implications by regaining your citizenship as taxation is based upon where you reside - except for the USA where you are liable for US tax no matter where you reside - and they are VERY good at collecting it. There are protections to avoid double taxation but it does get complex quickly so a good experienced tax accountant would be a good idea before contemplating moving to Spain.

Definitely do it now. Who knows what might change with Spanish immigration policy and your personal circumstances and desire to move to Spain.