Is it a good idea to mention any freelancing experience in the cv?

Yes why not, write what ever the expertise you have.

Yes you can, but remember few things

Make separate headings for full time experience and part time experience. The freelancing experience is part time experience. Many professionals nowadays write there academic qualifiaction and professional certification under separate heads. It makes cv more readable and understandable.

yes it is good n possible, during recession many individual lost their job n work freelance or work in any other business or field etc.

Of course. Employers are not interested in the number of hours you sit at a desk but in the skills you have and the work you have done so far. 

yes

under work experience part.

either combined with employed exp in a time line manner or separately one column for employed section and one for freelance