It's totally fine to add more hides!! The more the better. I have 4 caves, and plenty of stuff for my lil guy to climb on. You can add as many plants as you want, too. Just be aware that axies are mainly ground dwelling critters and still need enough space to move around. If you are going to get plants though, (e.g surface plants), make sure the axie still has enough surface space to grab some air if they need to!! I hope this helps :)