You should start by getting lessons with a professional guitar teacher. Why not give yourself the best chance for success? Find a way to do it.
>>I heard I need to know how to tune my guitar,...<<
Yes, that's true. There are thousands of videos on YouTube to help you. Get a Snark clip-on tuner.
>> I need a guitar with the right neck size for me,...<<
You just need to get a full size guitar. It'll have the right neck size.
>> I'll need extra strings,...<<
One full set plus two extra high E strings (beginners tend to break them - every music store sells individual strings).
>> and all kinds of things.<<
Not too much else. A few picks, a strap if you plan to play standing up, and eventually a capo.
Playing guitar for 55 years