I just want one main query clarified: To view a city's stats, I must infact own that city? 'City Inventory' I suppose refers to my own. So if I am considering buying, say, a tavern in a city I don't own, there is no way I can see how efficient it will be because I can not look at a city's stats? Or maybe there is a way, I am just unable to find it? (probably not)

Actually, when it comes to how well a tavern (or any other income facility) its the overall morale and crime of the planet, not the city.
And to answer your question, yes, owning a city will give you those stats.

On the city level, the only thing you have to worry about is the number of a particular facility in that city. A city flooded with 20 taverns is most likely going to give out really bad facility income.

Ahh, well that's my query clarified. Thanks. Actually, just to (sorry to repeat myself) clarify, to know how well a facilities income will be I need to know the crime rate and morale of a planet? Yet I can only know that how? By owning a city on the planet? Which I think is what you said, so actually, if I do build a tavern on a planet that I don't own, I will be doing it blind so to speak. Unless i can see a planets stats (crime and morale) some other way. Ultimately I won't know how good a facilities income is going to be until I've actually built it? (on a city I don't own)

Knowing the crime and morale of a planet help, but are not going to perfectly tell you how much money you will make. There are a lot of different factors involved.

There are 1 sure-fire way to get the crime rate and morale of a planet. Own a city (any city) on the planet.
There is one way to estimate crime rate and morale, and that is to scout it out, recording every building and use the equations on the Rules page to crunch the numbers yourself. However, if the tax rate has been changed, the numbers will be off, possibly by quite a bit.

“Ultimately I won't know how good a facilities income is going to be until I've actually built it? ”

Well, there is one other thing you could try...
find someone else that owns, preferably, a tavern (or whatever you plan on building) on the planet. See if they would be willing to tell you how much they make.

Clarity acquired, thankyou Roy Starkiller.

Silthar, if you're building on the planet then it will tell you who owns the city from the build permission (if it's accepted, at least) and you can ask them what the stats are. You can also try contacting the controlling faction, because chances are they own at least one city on the planet. Be specific about the planet you're enquiring about.