Who is eligible to participate in the referral program?
Anyone who wants to earn money can take part.
Are there any additional requirements for these users? let's say a certain amount in the account or use of the wallet for a certain time, etc.
For now there is no any additional requirements.
Is it possible to combine cooperation at the same time, that is, to be a customer of a service (seller) and register in a referral program?
Yes, you can get rewards from both programs.
I know softswiss company as a very reliable one. That's why I sure that coinspaid is worth of attention. Good luck, guys
softswiss is reliable? is it joke mate?

I dont quite understand you. Can you rephrase your question?
In what format will the user be notified that his hot wallet has reached the maximum limit?
There is no such function. But if this is important for you - contact the support team, we will come up with something!
Are you planning to implement the conversion of coins into dollars? Since the dollar plays a dominant role as a means of international settlement.
Perhaps in the future such a function will be available.