I am not supposed to place an answer here, as I am no more active in this site: however, a comment doesn't offer enough place.
So, you ask:
1) "spin is a property of the wave function, and not of the particle?"
Please pay attention to the following differences between the standard quantum theory (SQT) and the Bohmian interpretation (BI):
SQT doesn't work with the concept of particle, but with the concept of wave-function. When we send the wave-packet onto a detector and we get a click, a recording, we say sometimes "we detected a particle". This is not a rigorous expression from the point of view of SQT, we should say that "we got a detection". There is another concept valid from the point of view of the SQT, "type-of-particle", which comprises rest-mass, spin, charge, and others. I'll elaborate more, in continuation.
To the difference, BI distinguishes between two concepts: the guide-wave and the particle.
Now, some clarifications. By solving the Schrodinger eq. we get a wave-packet. SQT says that all the properties of the type-of-particle are displayed at every point in the wave-packet. This is all that the SQT gives us. (Of course, when we measure some observable, position, linear momentum, spin-projection on some axis, i.e. when we do the classical measurement (i.e. with the macroscopic detector), there come decoherence and collapse, but our talk here is not on this.)
BI also recognizes the type-of-particle properties, and they are also carried by the wave-function which is considered a sort of guiding wave. To your question, spin is considered to be carried by the wave-function. When you split the wave-function according to the spin-projection, each separated wave-packet carries one of the values of the spin-projection.
What then is the Bohmian particle if all the type-of-particle properties are carried by the wave-function? Different followers of Bohm say different things. Some of them say that the Bohmian particle is a special point inside the wave-function, with the property that makes a detector click. When we split the wave-function into space-separated branches, only one of them is supposed to take the so-called particle. However, Basile Hiley (a friend of Bohm that collaborated with him in some articles), told me that he sees the particle rather as some sort of structure.
Anyway, this point, or structure, etc., is supposed to have at any time a position, and a Bohmian velocity. These are all the properties that the Bohmian particle is supposed to possess. The Bohmian velocity multiplied by the mass of the type-of-particle gives a Bohmian linear momentum. If the wave-guide displays a well-defined linear momentum, then the two linear momenta coincide. But if the wave-guide doesn't have a well defined linear momentum, the Bohmian linear momentum is not equal to the average linear momentum displayed by the wave-guide.
I also saw your question
2) "if a bohmian particle only has position, how does it interact with other bohmian particles to transfer momentum? Surely the bohmian particle itself has momentum as well as position, right? Which would mean that properties of the particle are at least mass, position, and velocity."
NO!!! It's not the Bohmian particle that interacts with another Bohmian particle. The wave-guides interact, exactly as requires the Schrodinger equation. We get a two-body wave-function - wave-guide - that guides the two-particles. And the two Bohmian particles have, each one, at any time, position and Bohmian velocity.
FINALLY to your question
3) "Answers to my question here seem to say that the imaginary position of the bohmian particle actually has nothing to do with "where" the detector detects the particle."
That's exactly opposite. Exactly for this purpose was built the BI. It was proposed as a tentative to get rid of the collapse, i.e. that part of the wave-function that comprises the Bohmian particle, that part makes the detector to do a recording. See my explanations above. The detector is supposed to produce a recording iff the Bohmian particle passes through the detector, and at the time when it passes.