A few questions re 0% transfers

Em1982

I am hoping to transfer some of my debt to a 0% credit card and I have a couple of questions about it. Firstly, I am going to close two of my old credit cards in order to reduce the availabe credit I have, which I'm hoping will help my application. If I do this does anybody know how long they will take to appear on my credit report as closed?

Secondly, the advice tends to be not to make multiple credit applications in a short space of time, can anybody clarify exactly how long should be left between new credit applications?

Any replies would be greatly appreciated

Emma