I have a flight from Bangkok to Rome by China Southern with a long transit (7 hours) in Wuhan.

I‘m not sure that and you'd better prepare some cash. There are the automatic teller machines in the airport and you can deposit some if you need. There are many restaurants in T3 and you don't need to worry about that. If you choose the restaurant in the transfer zone, you don't need to check in. If you eat out of the transfer zone, you have to apply for the stay permit at the airport.