May user make pruchases in application using their credits that were bought outside the app?

I have read App Store Review Guidelines many times, I just wanted to ask to share your own experience with following use-case.

I have app for selling digital content (photos).

In-app purchases are really not suitable for this kind of app, as people are selling content to each other and they are the ones receiving the money for the content. Every user has its own balance and can top-up it up or withdraw the money to real bank account.

Users are able to top-up their account balance from the website-based app. I am thinking about removing the option to top-up the balance in App Store app altogether, with only informative text claiming you must visit app's website to obtain more info about topping-up the account balance, without using links or other CTAs.

1. Does the rule 3.1.3(a) “Reader” Apps apply for this case? If so, is it still possible to use your account balance to purchase digital content? OR
2. If you cannot purchase digital content using your account balance, is it still possible to at least offer digital content via App Store application without implementing IAP (meaning user is requesting something, not making any credit (money) yet)?
3. If Apple sees some kind of account balance in user's profile, will it demand implementing IAP in all cases?

Thank you for the response in advance.