EU citizen/US spouse residency issues/capital gains/taxes

We're leaving for Spain in a week and are starting to realize some of the bureaucratic difficulties we can expect to encounter.

We may have made a mistake in choosing a relocation service and a lawyer, as they are still having to "research" some of our issues.

Some background: I am a dual US/Austrian citizen. I have passports to both countries. Retired on SS disability.

My wife has US citizenship. Retired physician with a state pension.

Here are some odd things we're being told:

I of course have the right to stay in Spain for as long as I like.

My wife is restricted to a 90 day tourist visa until we both go through the official residency process. I'm assuming that she can leave the Schengen Area, wait 90 days, and then re-enter the country for another 90 days.

Here's where it gets really strange: we were advised not to sell our house in the US the same year as we apply for residency, because for some reason Spain gets to double tax us for capital gains, or their equivalent.

In addition to this double dipping being unfair, this seems to be incorrect.

Anybody run into something similar, either real or imagined by uninformed Spanish lawyers/tax accountants?

Edit: It does appear that I need to get the NIE or EU certificado first. Still unsure if she can come in to the country on a tourist visa and then have this changed once we are in country. Our "lawyer" (who I'm going to dump once I find somebody competent) should know all this. If anybody has gone through the NIE or EU certificado process and can speak to this, I would be great to hear from you.