Excuse me if this is a bit of a repeat of what has been said above, but I am just on my first coffee.
Before you start fiddling with things set the base with scaling and font scaling factor:
Settings>Display>Scale>
I like 100% for 1080p and 200% for 4k but my eyesight isn't the best.
Scaling looks pretty good on you screenshot, so leave it.
Fonts;
Tweaks>Fonts>Scaling Factor>
I use 1.25 for 1080p and 1.33 for 4k
Now for the default fonts. I just did this yeasterday, and I remember the default being 10. I usually use Noto Sans Regular, so I just increased the size to 11 in the tweaks screen.
Still, you are right, the top bar could be thicker. There is an extension - Maybe "Open Bar" that will let you do that.
As for the Activities button "Hide Activities Button by zeten30" or "Just Perfection" can handle that.