What is the Difference between Watashi in Hiragana and Kanji?

My first question is about the lesson below.

I was wondering about" わたしは さおりと いい ます". Is " と いい ます" informal way of saying" わたし はさおりです".

My second question is about the usage of watashi in hiragana and kanji in the lesson below.
わたし 私

Is it optional to the person to use the hiragana or kanji version of the word.

ます and です are polite / formal way of speaking. いいますis the verb “to say” but is the polite way of saying this.

Have a look at this website it has helped me a lot to understand the basics:

The lesson is just providing an example of both わたし and 私. Although most of the time you will just see 私 in more advanced lessons.

私は、太郎です。(I am Taro.)
私は、太郎と言います。(Ich heiße Taro.)
私の名前は、太郎です。(My name is Taro.)

それなら、あなたは美味しいですか?

“If that´s the case, are you delicious?” xoxo

Domo arigato Yutaka! I don’t have a Japanese keyboard on my computer, but I do on my Tablet.

Thank you very much RichAus for the Resource. I’m very appreciative for your help.