I think 係度is not necessary in a lot of sentences. 

But係度can make the tone of sentences stronger.

係度 can mean here/or doing something in usual.

If you live in Hong Kong, people will more like to say hi/hello to you.

If you have a really good friend , maybe he/she will say 點呀 to you.

Something like asking ‘how are you?’.

點呀 is a informal word, a little bit rude .

If the stranger say that to you , always no good things happen.

喺度 originally means "here" as in some of your sentences. Yet the usage of this phrase can be "figurative", ie there is an extended meaning for emphasizing "right now":

Barbara 係度睇緊報紙 -   Barbara is reading a newspaper - extended meaning "right now"

我係度做緊嘢. 我唔係睇緊電視 - I'm working. I'm not watching TV.  - extended meaning "right now"

Quite a number of phrases in Cantonese carry extended meanings (which is common in natural languages). The extended meanings can be dominant over the time. :-)

Another example of dominating extended meaning of a phrase: 實 . it originally means "firm" but it can be used as an adverb for "definitely".

佢實死無生 he has no chance to live

Hope it helps~

From my understanding, it isn't required; however, it does indicate location. 

For example, 佢係嗰度食嘢 = He/she there eat things. (My grammar maybe off a little) 

                        佢係度食嘢 = He/she here eat things.

Yet, you could just say 佢食嘢 = he eat things.

I've have been using Glossika on and off. While I find it very useful for improving listening and fluency, some of the sentences are overly complex and sometimes the grammar is a little English sounding. Cantonese grammar is actually very simple, to the point that it seems there are not enough words. In addition, Glossika uses some very English phrases that I haven't really heard anyone say in Cantonese. 

If you are near TST, there is a good bookshop called Swindon Books that has some good books upstairs. The publisher is Greenwood Press. It is always good to use various materials to get exposure to the language.