Quite often the interference is because the receivers are poorly designed to resist otherwise legal an well maintained transmitters. Doppler direction finders, such as the MicroFinder, do not receive radio frequencies directly. You must supply a narrow band FM receiver for the frequencies you are interested in. Many T-hunters use scanners or surplus HTs. The MicroFinder does not come with a transmitter of any sort.
Many hams use HTs that have built into ruggedized boxes, with an appropriate controller.
All the parts in the kit are there for a purpose and aren't optional. Yes you can. The MicroFinder is designed to accept Roanoke style four-element antenna arrays, but you can build others with six or eight elements. Not at this time. The embedded software is written in H8 assembly language and is not currently accessible to casual programmers.