> Would I be correct in saying OCaml is pretty much Rust without the borrow checker?

Yeah, it's very much on those lines, though the syntax is a bit more ML-style (Rust pushes a bit towards a C-like syntax).

(I actually mostly use Scala myself these days, but I know the JVM is a dealbreaker for some people, and the design compromises for the sake of Java compatibility mean Scala is probably not the best choice for a first ML)