Reddit mentions of Alfred's Basic Adult All-in-One Course, Book 1: Learn How to Play Piano with Lesson, Theory and Technic: Lesson, Theory, Technique (Alfred's Basic Adult Piano Course)

You can buy a second hand fullsized casio keyboard to get you started, they will be pretty cheap. If you end up sticking with it, then spend some time and money on a good one.


This is a good book series to get you started;
https://www.amazon.com/gp/product/B017OBN7CK/ref=dbs_a_def_rwt_hsch_vapi_taft_p1_i0

There are many. Pick one with good reviews that looks good to you and get started.

Also, check out this book.

And, as someone who has been playing piano for over 30 years, I recommend that everyone who is interested in learning an instrument find a teacher. It is so worth the money. You can even check out a local college and find a graduate student in music to teach you. You can find people who will give lessons online.

Things you will learn from a teacher that you will not learn from books and videos:

• A good technique that will make it easier to play and help you avoid accidentally injuring yourself
  
• Learning effective methods of how to practice
  
• Guiding you through a repertoire that will keep you interested and steadily progressing
  
• Pointing out any personal shortcomings or weak spots or bad habits in your playing (and training you on how to fix them)
  
• Giving you accountability and something to shoot for every lesson
  
• Providing personal encouragement
  
• Building (hopefully) a great relationship and someone to share love of piano with
  
  Good luck and have fun!

I found this one:
https://www.amazon.com/Alfreds-Basic-Adult-All-Course-ebook/dp/B017OBN7CK/ref=tmm_kin_swatch_0?_encoding=UTF8&qid=&sr=

But is seems that it is focused on piano lessons, does someone know if it have a reasonable amount of music theory as well? Is it enough?

It sounds like you haven't tried yet, so why give up before even trying? Playing any musical instrument is going to be hard and having a teacher would definitely help, but if you've got the motivation and tenacity, it's far from impossible. If I'm not mistaken, several posts here have been made by people who were self taught.

Of course, I had a teacher as a kid, so perhaps if a self-taught pianist could back up (or refute, if that's the case) what I'm saying, that'd be great.

PS: This seems to be a good resource for starting out:

https://www.amazon.com/Alfreds-Basic-Adult-All-Course-ebook/dp/B017OBN7CK/ref=sr_1_2?crid=39FU4MO6QNQ7E&keywords=alfred%27s+basic+adult+piano+course+level+1&qid=1550941821&s=gateway&sprefix=alfred%27s%2Caps%2C305&sr=8-2