Barleywine
Virtually all the Horary books this century have used the Traditional planets only. Generally though you don't have to use all the planets, not even all the visible planets. You should only use those house rulers relevant to the querent and the quesited and any planet that is either in the relevant house or aspects the relevant significator for better or worse. Other than that, you only check to see if another planet will frustrate the perfection of the matter (usually by aspecting one of the significators before the other significator does).
The problem with going beyond the significators from the question is that you can lose sight of what matters because you start to examine non vital factors in detail.
Clearly if someone asks you 'Will I get the job I applied for and will the salary be good?' then there are potentially three planets involved in answering the question. The significators for 'Will I get the job' and if you decide that they will, then the significator for their income or cash flow (Lord 2).
Other planets would only be considered for signification if the question was more complex. This of course does not nullify aspects from benefics or malefics, either by nature or by accident.
So if the significator of job and querent are applying to a trine but Lord 6 aspects the querent's significator first, that might signify that he or she will be too ill to go to the interview, or fail the medical (if there is one) for the job.
Thanks for the tutorial here. I had forgotten that the planetary aspects aren't "frozen" like a natal "snapshot," but are instead moving toward or away from "perfection." "Applying" and "separating" I got, but not the "next aspect" thing, except in a vague way. This has been a good learning exercise.