Astute, practical advice. Very close to what I did to become fluent in Spanish and to read French, Italian and Portuguese for a graduate degree. One reason it is easy for young people and difficult for adults to learn a new language is physiological. (You may have touched on this and if so I missed it!) There is a part of the brain that is “flexible” up to adolescence and “hardens up” after that. Language learning is in that part of the brain. This is a simpistic explanation but well documented in finer language in the literature. The important point — and you made it — is that it may be more difficult but it is certainly possible and the rewards are incalculable.
The French have a saying: “Pour chaque langue que l’on parle, on vit une nouvelle vie. Celui qui ne connaît qu’une seule langue ne vit qu’une seule fois.”