Get a dictionary and look it up. My other tip is to keep a master deck of new vocabulary you find. First add new vocabulary into a small new desk, go over them for a while, then add them to the bigger deck, the bigger deck is the challenge, but it's good to build on things as you go along or find a deck with words for beginners and build on that. It helps to use the hiragana you've learnt too, for the readings, maybe the layout of the cards isn't the best for you? Get out a pen and paper and break it down into words. But be warned that not all the typical phrases can be translated directly.

Sounds cool but a lot of natives tend to use LINE instead. :)

〜と言った。 is a predicate. と is used like a quotation particle. So it's like: as for this person, they said this. スーさんは猫が好きですと言った。 Sue said she likes cats. As for sue, she said she likes cats. Same goes for と思います。 スーさんは猫が好きですと思います。 As for sue, I think she likes the cat. I'm not good at explaining because I just learnt this myself but search up what a "predicate" is and it will help you understand a little more. I hope it helped a little. You can find this in chapter 8 of the Genki textbook if you have it. Send me a message and I will send you the information I have on this subject. :)

One or two hours a day. Spend time each day first working on practicing what you learnt the previous day and then move onto the new stuff. Repeat. It's helpful to post notes here or on lang 8. You can find language partners. I think Genki can help with reading and writing and possibly listening but you really need to find someone for speaking practice. :)

You could certainly try there are a lot of exercises and a lot to learn. It's good to practice it too. I think it would be quite intense but it's not impossible. Just pay attention to how much practice you give each section.

It's short for のです. I think it's when a speaker is explaining something or wants an explanation for something they are talking about or about an event currently is happening or has just happened.