Using component state for form data is also worth considering. However you decide to manage your form data, it should work well alongside Redux Resource.
Using Resource Slices
You can also store form information inside of the resource slice. A Redux best practice is to separate your client-side data from your server-side data, so form information should be kept separate from the actual resource objects themselves.
Instead, you might choose to use meta for form information, or perhaps an additional "top-level" key within the resource slice, such as forms.
One thing to consider before going with this approach is whether or not your form allows a user to modify more than one resource at a time. If it does, then you may want to consider storing the form data outside of an individual resource slice.