I think 5,000RMB is enough for two people traveling Guilin for one week, excluding your airfare. Well, actually, you could spend two days in Guilin and then go to Yangshuo or Longsheng for the rest days where is much better for a honeymoon. You could book a local hostels which is reasonable enough.

March is still a little cool in Guilin, especially when you taking the Li River Cruise. So, please prepare thin sweaters and jacket. Hope you will not have the successive rainfall then.