Citing a collection of work (i.e. literature review) by 1 citation?
Do not automatically cite everything X has cited. You should only cite a paper you've read, and it will be assumed that you have read everything you cite. Author X could have made a mistake, misunderstood something or deliberately misrepresented something.

Whether it's worth tracing back every reference cited in X's paper depends why you're referring to it. If your paper describes an alternative model and the differences can be traced back to, for example, the data sources you've used, then you should go back to them, read them and cite them; ditto if your paper is a critical review of X's model. If you're simply using X's model out-of-the-box you don't necessarily need to go back and pick over every source for every parameter estimate.