Would you outsource... your outsourced work?

If the project requires multiple skills and you don't have all of them then you can get it done by outsourcing that part of the project you don't have expertise and doing the rest yourself.

About outsourcing the entire project, in my opinion it's ethical if you let client know about it. Many client don't have time or technical abilities to manage projects by interacting regularly with the workers so it would be nice for them if they have someone experienced in project management to handle the task and get it done through best possible resources.

In fact, I am planning to do something like this where I will accept the projects, get them done through workers from freelance sites and deliver the end product to client taking complete responsibility of quality and deadline.

It's not always possible that you have all the skills necessary to handle the project especially true for software projects and in that case it should perfectly be acceptable by client if you would like to outsource some of the work. Being a project owner you are responsible for the quality of the outsourced work. I don't see any reasons client should bother about if they are getting the quality end-product within their budget. The cases you are talking about may be small tasks where client wants them to be done by the freelancer they are hiring.

After working hands-on for years it's a logical step for you to graduate to Project Manager. Handling medium to large scale project definitely requires such role and it would be a challenge to handle such projects with virtual resources.

Wish you the very best Marissa :)