Thank you for the answers. They helped me. I think a got a bit scared because I read all these threads online which said roaming is due to bad husbandry or hunger.
I haven't handled him yet. I only put him in his cage (when he arrived and when he escaped) and I actually don't plan on handling him very often.
Right now he is sleeping anyway (he went to sleep about 20 minutes ago).
And concerning the appointment:
I've read a few books before buying this little ball python and all of them said to do about 2 faecal inspections (if that's the correct english term for it). And within his first hours I had a sample. I called to the (reptile-)vet and he told me to bring it and the whole animal. That way he could do a whole inspection. It'd be wiser and since I was a bit flustered I just agreed. That's why I have an appointment but I might cancel since I feel like there is not really a reason to go other than that he might weigh a little too less in which case the vet wouldn't be able to do a lot either.