The main pitfall, fit-wise, is that the top tube is too long on the donor MTB to make drop bars workable. But that Ritchey looks like the TT is fairly short.

This may be countered by what looks to me like a fairly laid back ST angle.

Component-wise, the Ritchey has cantilevers so no need to use V-brake travel agents for the Tiagra STI
levers.

Here's what I'd do. Measure up a bike from the RJ stable with a fit you like, and see if you can replicate the fit coordinates on the Ritchey. If it's doable, then build it up. If not, looks for another donor frame.

I did something similar this winter, from an abandoned Focus Crate Lake hybrid frame. It works well, I got the position I wanted, but the steering is very, very slow.