Teach yourself hiragana and katakana first. I recommend two books by "heisig"

once you you do that you will start to have a good feeling in how you want to start studying. I didn't start learning Japanese until age 37/38 and have used many different tools including itaki. 

a one semester college course also might be helpful just to get going but if not available itaki might be a faster way coupled with good study materials. 

Hi!!!! there are very good Japanese tutors on here at italki. You just have to pick one you're comfortable with and understands your goals. Genki 1 and Genki 2 are excellent beginner books. I highly recommend them. A few teachers on here also use those text books. I think you should take a class or start here on italki. You need a native or near native speaker to correct your pronunciation and help with grammar. You don't want to ingrain bad habits early on bc they will plague you and be hard to break later.

There are 3 writing systems (Kana) that include katakana, hiragana, and kanji. Always learn hiragana and katakana first. Kanji mastery is developed over time. There are over 2,000 characters in Japanese Kanji, and remember Japanese students learn them starting in elementary school. 

You said youre an adult, so I'm going to assume you have a 40 hr a week job plus other responsibilities. Make sure you're learning goals are realistic. If you can't spend at least 5 hours a week practicing or taking lessens eventual fluency will be difficult to attain. Patience is the key as well as motivation. Take breaks to remind yourself why you're learning Japanese.

if you have any further questions I'm happy to answer them. Oh and yes in Japanese, depending on the situation is "Hai はい" and no is "ie/いえ". Now you know two words :)

Italki is for all levels. There are a lot of teachers who teach beginners. Theroretically, you can you the internet for all of your study materials. But there are many amazing Japanese study materials you would miss out on.

First learn hiragana and katakana. It took me a little over a month to learn, but some people learn it a few weeks. Make sure you know how to pronounce each sound, because some are very different than English. Then you should start studying kanji and basic grammar.

About a year ago, I was in your exact position. If have any questions on what to do next, there are a lot of people here who would be happy to help you. Feel free to ask me any questions you have as well. Good luck!