Hi!
I graduated from this course last year. I absolutely loved it, so I really hope you do too!
There are some tasters from some of the psychology modules on Open Learn. You can sign up and look at them for free here:
https://www.open.edu/openlearn/ - this is a good way to get a taste of the topics and the OU style of learning. There is also a course on there about preparing for undergraduate study, which could be useful.
Alison also has a few good free psychology courses:
https://alison.com/ - a good insight into the kinds of topics you will study during your course.
The counselling side only makes up quite a small part of the degree, with psychology being the main bulk (that's how they get their BPS accreditation). For this part, though, I would read about:
Person-Centred Therapy & Carl Rogers
Cognitive Behavioural Therapy
Psychodynamic Therapy
Basic counselling skills
BACP Ethical Framework
There are videos on YouTube, which are quite useful, or a quick Google search will bring up loads of results.
I hope you enjoy the course as much as I did!
Loren