I've been thinking about this as well. I really should, as a 50th birthday gift to myself and NZ as a whole, start to learn it properly

I highly recommend taking a class. Te Wānanga o Aotearoa has free ones that are generally evening classes.

There are other places offering courses but you'll probably have to pay.

The TWoA ones provide the Māori made easy book (and the sequel in the second year).

For flashcards, you can use Ankidroid. It has downloadable te reo set, but I think it's better to start empty and add your own words and phrases as you learn them in other places (course/book/etc).

I highly recommend The Wānanga ō Aotearoa (TWoA).

I did two courses, one evening per week for two semesters each (over two years). Actually did it at work with about a dozen other colleagues.

It was awesome. A perfect blend of the technical aspects of the language, actual usage, cultural background.

That might be more than you can commit to, they also have many other courses in smaller more manageable chunks.

I used the Drops app (https://play.google.com/store/apps/details?id=com.languagedrops.drops.international&hl=en&gl=US&pli=1) for a while, but it was mostly just vocabulary, and may not be entirely accurate :-/

I also watched some Toku Reo online https://www.tokureo.maori.nz/ There are hundreds of episodes with Grammar, Vocabulary, and Activities sections in each episode and online exercises to practice after each episode. There's also a short version of each episode.

I'm probably not the best person to give recommendations though, I've made very little progress...