Is it unkind to keep fish in a tank?
If you do it properly then you can keep them healthy. Get the biggest tank you've got space for so they've plenty of room. There are ways to be more fish-friendly such as not buying fish that have been linebred (like any unnatural colour forms or ones with extra finnage or weird body shapes) and buying ones that are locally bred so they aren't flown long distances or taken from the wild. This will limit your choices but it'll help you sleep better if you're worried about it
I'm no fan of animals in cages - isn't fish in a tank the same?
Pretty much but you've total control over their environment so in a way it's even more confining. You'll need a water test kit so you can keep it in good condition. Healthy water, healthy fish.
Do they live long?
Depends what sort you get, some live less than 5 years, others can live over 30 years. Most small tropical shoaling fish will live about 5-10 years.
Are they high maintenance?
Yes. And expensive. Don't listen to anyone that tells you fishkeeping is cheap and easy.
How often would we clean them out?
Once a week is usually about right but it depends on how many you have and how big your tank is. Smaller tanks (which are harder to keep than big ones!) need cleaning more often because the water chemistry is less stable.
Are all the pretty colourful ones tropical?
No, there are a few colour coldwater ones but I wouldn't recommend goldfish unless you've got a huge tank because they get massive.
Are tropical fish harder to keep?
Not if you pick the right ones to start with and do lots of planning.
What other questions should I ask?
Anything and everything and check all your advice with different sources. Pet shop staff don't need to have qualifications (in the UK anyway) so they don't always have the answers. Best to get yourself a couple of books or go on a fishkeeping website to get specialised advice.
What should I know?
Keeping fish is more complicated than most people anticipate but it's loads of fun if you like that sort of thing.