Build up a business where you consult / contract as a mechanical designer (UK)

[Searc]

I am currently a mechanical design engineer contractor PAYE through an agency (UK). Speaking with a colleague at work where his contract is coming to an end. His plan is to only take on roles through his personal service company and build up a group of clients over time. His plan is to effectively build a consultancy business where he will jump between a number of clients providing design services.

1. How common is it to be able to continually contract through your own company (i.e. outside IR35) as a mechanical designer (manufacturing)

2. How realistic is it to build up a company where you effectively consult for a number of clients (perhaps not at the same time) in mechanical design (manufacturing)