I'm planning to stay for four days, one in the city, every day I'll have pay the entrance fee?

If you just stay in the mountain without going down, you can stay for several days and you don’t need paying for it again.

If you wanna get out and re-enter, it is suggested to apply for a re-entry permit when buying the ticket. By showing the permit, you will be allowed to enter again.

Thank you so much for the reply, I really appropriated that. Just one more thing, I'll be traveling with two back packs, one of those I'd like to store in some place and just when I go to Beijing get it back, for convenience. Do you know some place that offer this service? Again, thanks!

Oh, I get it. Both at the airport and railway station, there are luggage storage counters/offices. It is fine to store your luggages there for several days and it is safe enough.