Work remotely for european client

I have a Stamp 4 visa as a critical skills worker. I am looking at the possibility of working remotely for other European client while continuing with my existing full time job.
Remote job is just for an IT support, as and when there is a requirement and hence i am not interested to give up my full time job. Can anybody suggest the pros and cons of that.

Also is that ok to setup own company ? Do i need to give up my full time job if I setup my own company

If you are on an Irish payroll, of course you can do anything (either have a second part-time job or start a new business yourself).
If the employer posts money to an Irish based employment agency, and the agency sends money to you, you need to check with the agency to see how that is arranged.
If the foreign employer sends money directly to you, you will need a valid work permit for the other country that the employer is located in. You can work around this by setting up a business in Ireland, and basically 'sell' your business to the foreign employer. I've see many people do this for tax purposes (Ireland has a much lower corporate tax).