Retirement tax questions

Thanks!

 

I’m not an independent contractor, I go through a middle-man (company) from gig to gig and am a W2 employee of the middle-man, which can change with each project. On one project, the middle-man provided a 401k. On my current project, they don’t. Not that this changes anything.

 

It sounds like maybe I should just put the money I would have put in a 401k into my Roth IRA? Does that have a limit?