comparison between tax and ni contribution

hi
Respected all

I m posting this question from my friend, who is on psw visa, and currently working for a company full time. His concerns are how to prepare himself and make eligible to fulfil all necessary requirement to successfully lodge an application for tier 1 general visa. He fulfils all other requirement a part from earnings, and for that need ur advise what is the economical way in terms of paying tax nd ni either opening up a limited company or find a 2nd job.

He heared that if u do 2 job, ending up paying much tax?
Comparing paying tax nd ni on 2nd job
Nd paying tax nd ni ön a limited company which 1 is cheaper, safe nd acceptable by the home office.

Are there any other ways of doing earnings 4 this purposes?
Also considering ny future changes into tier 1 general. . .

Plz gv ur best advisd
Any comment wel come

Regards