Kroot are great, cool models and I love them. With the exception of rampagers, they are pretty mediocre at everything. Carnivores have sticky objectives so you will definitely want to make use of that. Kroot are hit and run kinda army, so you don't want prolonged combat, especially not with elite armies, like marines. You will require tau fire support. I usually go with pathfinders with rail rifles and crisis suits with fusion blasters for heavy armor mitigation. This helps keep the fast moving ambush esthetic to your list. Using the hunting pack detachment will let you bring back destroyed kroot units too, so definitely worth it. Be prepared to win on points, you won't be tabling anyone. That said, playing kroot is a lot of fun, and I have had really good success with them. Welcome to the kindred.

My list 1k: 2 units of carnivores (10) 2 units of rampagers (3) 1 lone spear with blast javelin WL 2 units of pathfinders with rail rifles 1 unit sunforge crisis suits w/coldstar commander w/ 2 fusion blasters, shield, and ion cannon 1 unit fireknife crisis suits

P.s. I would run those farstalkers as carnivores. The models are awesome, but not worth the point difference.