As far as I remember adaway is the og adblock for android, it is available on f-droid and pretty much the only app that I used since ever, and one of the few reasons I still won’t let go of rooted phones, https://adaway.org/
On top of that I would recommend you to run your own DNS server with unbound, add to that pi-hole and wireguard and you have your own pi-hole set-up on any device you want.: https://docs.pi-hole.net/guides/vpn/wireguard/overview/
It’s fine. “Only 27GB” is hardly too small for the system, even a bloated system wouldn’t take that much space.
But if you must have a larger partition I think a reinstall would be easier, resize the partition is possible but because of the encryption not a straight forward thing. I wouldn’t bother really.