quote:

isn't part of the custom is to symbolize the "4 corners of the earth"?

I've seen some hold the 4 tzitzis starting from even earlier.

The Be'er Heitiv 59:3 brings a custom to hold all 4 tzitzis from the words "and may He gather us in from the four corners of the land" at the end of Ahava Rabba. I believe that the source for this comes from Sefer HaKavanos of the Ari zal.
However, Shulchan Aruch 24:5 writes to look at the front 2 tzitzis, and the Maharshal and Vilna Gaon also agreed to this.

quote:

And speaking of sitting or standing for shema, ashrei seems to have some ambiguity.

quote:

As far as I can see, if there is no minyan then you only need to stand for the Baruch SheAmar, Mizmor LeTodah, Yishtabach, the Amidah and Aleinu. Everything else can be said sitting down or standing up.

I couldn't find any source who requires standing for Ashrei, but the same sources who reccomend standing for Mizmor LeTodah also reccomend standing for Az Yashir. Many are of the opinion that both may be said sitting.