What is best way to clean/manage MacMail on Mavericks to speed up loading?

Hi,

I am using Macmail on Mavericks, on my MacBook Pro. I have tens of thousands of emails in many different folders (I use this computer for my business) and I would like some help/advice on the best way to manage the mess. I have lots of folders, and mail inside of those folders. I use this client to collect mail for at least 8 email addreses.

I am assuming that the spinning ball is because I need some serious house keeping here, but am not quite sure where to start. I have seen it both recmmended and advised against to use cleaners, delete caches and logs, etc...Should I just archive all old mail? Is there a better way? If I do archive the old mail, do I need to do something to "reclaim" the space?

Sorry to be so vague; I am at a complete loss here. I don't want to achive thousands of emails only to find this will not solve the problem.

Many thanks in advance,

Debbie