I recently moved to Barcelona with my gf and two dogs and we are considering starting our real estate journey with our first investment property either in Barcelona or Valencia.

@Mike Levene cost to build per square foot is $200-$300 depending on finishes.So, you can start with that.

I'd start with picking one city and spending a lot of your time to do a deep dive building relationships and learning different areas.

I believe I've heard about $120/sf for the cost of building.

I mentor a few investors especially just starting.  

Once you start to get people in there to look at project to project, that will give you a baseline then you'll start to gain more knowledge on where you need to be on the pricing/estimates etc.

We recently relocated to Phoenix last summer and I'm starting to look for recommendations for local credit unions here in Phoenix which are trustworthy, low rates, personal touch, easy/simple to work with, etc. 

What class of building? 

Since you're looking to expand into Florida and other states, I'd recommend starting by narrowing down your focus:Market Research – Florida has great opportunities, but each state and city has different laws, taxes, and demand drivers.

Starting looking for opportunities last Fall and so far it's been terrible.