Hi rohitanna
1) I would send only 3. More would be pointless. Some schools state recommended 3 and maximum 4. If 3 won't do the job, 4 won't either and you'd just give the adcom more work.
2) You should have Letters of Recommendations sent by whoever writes them. Most US universities use online forms for letters of recommendations.
3) The research experience would be more important if you were going for a PhD. If you don't have any I would definitely write about why you're motivated about getting an MS and what do you want to do with an MS after you get it. You should definitely mention your final year project. You should also write a paragraph of why you want to attend a certain school. The
statement of purpose for MS is much more stringent for PhD I think. When I applied for an MS my first paragraph was a general introduction involving my past academics. I went on to talk about why I wanted to get an MS in my particular fied as well as why I wanted to go to the school. I also wrote about what I wanted to do with my future after an MS.
4) Your
letter of reference should be 1 page max.
statement of purpose 2 pages max. some schools have specific limits so be sure to be under those limits. My standard was 2 pages max.