The answer is ‘it depends’. Generally you should go twice a year if your park is running fine. If I lived 4 hours from my park I would go probably 5 or 6 times a year - it requires a bit more attention.
Yes, you could work out a deal with a resident of the park to be your eyes and ears - you’ll need someone to call the plumber when there is a sewer back up and you’ll need someone to call you if there is an emergency, etc.
It could be possible to have your tenants pay online - however not all of them may have internet access or have a computer (like the elderly lady standing in front of me at the UPS store on Monday purchasing a certified letter so that she could get proof of delivery rather than track the package online). Another option would be to have them deposit their rent check into your business bank account. Most mobile home park residents pay with money orders… probably because many don’t have a bank account.