How to keep tax records for currency payments in paypal?

Question

PayPal

I'm going to sell goods from Russia to Europe, accept payments through paypal. On the tax accounting of these payments, I found only scattered, partially outdated recommendations, some of which do not seem to be very well developed. Judging by the answers of PayPal support to them, these questions are completely indifferent. It seems that there is no elaboration and established practice for processing such payments, and in any case there is a risk of running into a tax one. Has anyone done such a serious study?

Here are the questions to which I did not find answers, or they seem to me insufficiently worked out:
Are there any currency controls that are definitely not applied in any way?
Suppose, after the purchase, the exchange rate of the ruble fell sharply, the buyer decided to make a return, how can he return exactly the amount that he paid?
Do I need to arrange shipments somehow?
When is it more correct to carry out currency conversion and withdrawal of funds? Is it possible to store a significant amount in PayPal in case of a refund?