An easy method to determine whether such plants are likely to be successful where you are is to look around your neighbourhood and and see if they are commonly grown in your area. (Ignore magnolias, they are easier to grow on alkaline soils.) Though one needs to be aware of possible localised soil patches and boundaries - where I live the soil is quite different on the other side of the road. And of course the possibility of people having created special raised acid beds for them, or cleverly concealing that they are containerised.

In my humble experience, I don't think the presence of buttercups and dandelions is a decisive indicator of a non-alkaline soil. I weeded plenty of them out of my previous property which was on alkaline clay with flints. Though overall the weed population was rather different.

The other thing you need to be aware of is that some varieties of azalea need much more acid soil than others. If bilberries and heather aren't ubiquitous wild plants in your area, then you need to avoid the super-acid types.

A common reason for the failure of azaleas is that people buy the ones that are grown in greenhouses for the flower trade, and then think that they can grow them on in pots or their garden. Those ones are not easily grown outside carefully horticulturally controlled conditions.