I use the Newcomb's wildflower guide for here in the US - and Peterson's tree and shrub guides for work (I'm a forester). For the uses of the plants, I've used 'The Herb Book' by John Lust, but I'm far more of an expert identifying than using, so I can vouch for the efficacy of the two ID books I've noted but there might be something better for uses than the one I listed.
You are right, a lot of the species that we consider non-native invasives, especially the ones that have been here long enough to naturalize, like dandilions and chickory, are quite useful as foods or healing. Europeans brought them over specifically because they were so useful so that they'd have some things at hand that they knew they could use. Later introduced species, like mile a minute weed, Japanese knotweed and Japanese stilt grass were accidental introductions and those tend to be way less useful.