So recently I got to adopt a t8 pet :)

Questions I have are what's a good weapon set? Recommend scrolls? And highest opponents one can win against?

The hardest opponent you can beat is dependent on 1) weapons and scrolls 2) your pet’s build and 3) your perseverance

That being said, an evenly trained T8 could beat up very hard opponents and some extremely hard opponents. You’ll have to play around with different strategies to see what works best.

This is a great guide that lists all challengers and recommended tiers:

https://subeta.net/forums.php/read/893452/Comprehensive-Guide-to-Battle-Opponents-v2

Some good weapons for tier 8: cheap options

Expensive options:

Unlike weapons, scrolls are not tier dependent so the more you can equip the better. I have an end game scroll guide that gives recommendations for scrolls here:

https://subeta.net/forums.php/read/887189/Planning-for-the-Endgame-T10-Guide