[Help] Dialing in a Baratza Virtuoso for Espresso : Coffee

I just purchased a used Gaggia Classic, and I’m attempting to make my first espresso at home. At the recommend espresso grind setting of 7 on my Virtuoso, I extracted 70g from 16g in 10s. I kept grinding it finer and ended up at the finest setting (see pictures below). I ended up in the right range, but it tasted sour (17g in, 27g out, 26s)

1. Is this expected from a Virtuoso? I would probably be toggling between the two finest settings.

2. Should I switched to the pressurized portafilter?

3. Should I upgrade the grinder?

4. Would “temperature surfing” help?