You will also complicate all ongoing issues, from property tax protests to dealings with HOA to major improvements.

In some places, you can file a protest online.

In Tarrant County, you can also do a protest online and get an instant approval.

Also, the taxes on the house have increased and will be $5900, which would really eat into my cash flow unless I can protest at next opportunity.

Rather they hold protests against those "other people" in this case landlords as the villains of their story. 

I can protest the appraisal and I have done that with my primary home and will plan to do so with my rental.

Someone somewhere will find reason to protest or be offended 

However, Catalonia may be a little tricky these days (protests, aversion against tourists in Barca)...My dad backed out of Spain, but that was in the 70s: the apartment blocks he saw were too secluded back then...Anyways, good luck and hope you'll find something nice :)

Are taxes extremely high compared to nearby homes, and can be protested and lowered?

Appraiser has it at $73K even though the market has it at more like $65K which is infuriating because I thought you can protest tax rate when you get the bill but they said it had to be back in April when I supposedly got a value notice and they cut you off at 30 days to protest, for no reason except for exactly what did happen to me, people who dont know any better then get cheated by ridiculous property tax that they are powerless to do anything about.