Are there any differences in how new vs. well-established professors select students?
This will indeed  be highly  dependent on field. For instance,  in pure mathematics, there's a rather dramatic difference: most faculty don't take on any graduate students at all until after tenure.

The American Mathematical Society has written one of their culture statements about this issue. Generally, (pure) mathematicians have no labs and hence no need for bodies to fill them. And in math, on the time scale of a tenure clock, advising grad students is felt to have a net negative effect on research productivity (in the longer run there can be dividends). So the clear incentive is to wait until after tenure, and departments are usually fine with this.