It generally pays off in biomes with higher fruit yield like desert or when you have multipe fruit patches

I only research it if there are more berries than just the starting batch.

I wonder if I make a big mistake by never researching the fruit basket tech (basically the only one I don't), given that sources near the CC will be spent fairly fast, I prefer to put my resources anywhere else, and by the time I'm ready to gather other fruit sources I'm already drowning in food from fields... Haven’t tested if the speed difference you mention makes a big difference at the beginning.

Civilians gather food faster from berries and bushes, when compared to the fields. As Romans, you didn't need cavalry against the AI. Cavalry is only useful for hunting and rushes. You need good micro skills for the rushes. Ranged cavalry is much more useful for hunting difficult animals (elephants, bears, etc.)

Cartimandua would make an excellent non-combat hero, and unique. As Queen of the Brigantes, she was allied to Rome. Her bonuses could actually be tied to being allied to non-Celtic factions. If possible, say, something like being able to recruit a foreign unit/units, depending on the ally/allies (maybe she can have a unique structure that does it? No clue), representing things like when Rome sent a cohort to defend her from her former husband, or just some kind of broader generic bonus, but something the Britons otherwise wouldn't have access to on their own.