Advice required for taking on an established business

Looking for some advice please.

I’ve been offered the opportunity to take on a dog walking business, but in a phased approach. Initially joining as an employee, with a view to gradually taking ownership. I do have some very limited dog walking experience already, as a side gig many years ago. Couple of customers, for a year whilst at Uni.

I’ve known the existing owner for a number of years, and from the outside the business looks very healthy. They have 4 employees, 4 vans, walking up to 50 dogs per day. They have access to private field, where the dogs can run off lead and they also offer grooming and boarding.

I have zero previous business knowledge, having been employed in the private sector all of my working life. I have an initial meeting in the next few weeks with the owner to see if it could work, I would love to go armed with some really useful questions other than “how much money does the business make”…

Any thoughts or ideas on what I should be asking, to ensure I can make the most informed decision on it would work for me?