Hi Cactus (& Dave)
I'll start of by agreeing with Dave (and you thought I wouldn't?) Modern Astrology is too big a category to give a hard and fast answer, and indeed Traditional Astrology is not some monolithic whole. We tend (well I tend) to use the distinction more in terms of before Leo and the Theosophists (Traditional) and After (Modern) but in each there would be a very widespread and differential answer to your question.
Another thing that Dave and I both agree of is that the Astrological Alphabet is a curse for the beginner. Neptune = Pisces = 12th House is misleading, and any Modern Astrologer, worth their salt, will tell you that. Planets, Houses and Signs are different things and cannot be added together in some way.
I also agree with Dave (who has said this in various places) that trying to interpret one feature in a chart, divorced from the rest of the chart is to be avoided. Now for a beginner there will be a process of writing down a series of individual possibilities for each planetary placement, but there will be an attempt to try to integrate, or at least put these individual components into some sort of context.
With that caveat in mind - what could Venus in Taurus in the twelfth signify?
In your chart Venus is essentially strong in Taurus - it has the capacity to act, the twelfth placement makes it 'difficult' to act directly in your every day life - it's influence is behind the scenes, hidden from public view. That doesn't mean it's hidden from you, but it's not obvious to others, till they get to know you.
As you say Venus in some House systems is Lord 12. Even in quadrant systems where Lord 12 is more likely to be Mars, Venus has some rulership of 12 House matters, as Taurus is intercepted in the twelfth. The twelfth has rulership over institutions, prisons, hospitals, religious institutions and arguably large corporations, whose activities are 'shadowy'. Of these, hospitals are the ones that most of us come into contact with at some time in hour lives.
In quadrant systems Venus would also be Lord 6. The usual but not the only meaning of the sixth in every day life, is to do with illness and ill health issues (it also is concerned with your servants - now you might not think you have any, but it would cover any tradesman that you use - plumbers, electricians, car mechanics, etc). So Venus has some importance to health matters, especially but not exclusively in anything that requires hospital treatment. It might also indicate health problems which remain hidden for some time.
Going beyond that requires looking at the context of your chart, to try and identify HOW and WHEN such matters will be come important in your life, but one of the good things about the sixth and twelfth is that for most of us, ill health and hospitals are a comparative rarity. These Houses do not dominate our day to day lives, as the angular ones do.
OK, a few further comments on Dave's post.
I agree with him on Signs - one of the things that shocked me about traditional texts was that signs got a paragraph or two or three short paragraphs. Modern sign explanations ARE mainly useless, Element, Mode, Gender and Ruler are really all you need to know, plus directions and one or two other characteristics which you would use in horary or other specialised work.
I also agree on reading widely and doing as many charts and seeking as much feedback as you can, You will eventually settle down into a method that has a limited (compared to what is available) set of tools and procedures. You need to understand WHY you have chosen them and what their philosophical basis is. BUT start simple and work up - trying to take in every single modern, or traditional approach is going to end up confusing you - get the basics right first.
Where do I disagree with Dave - well we all know that and there's not a lot of mileage in arguing it here. I'd sum it up by saying just because something's out there doesn't make it important. If we take aspects as an example. With 7 planets thee are are a limited number of hits possible. Expand to 10 and the statistical probability increases, expand further and the hit rate increases exponentially. So if you add in Asteroids, Kuyper Belt objects, dwarves, etc -EVERY chart is laden with Hits and over a whole series of charts you can get enough hits to satisfy any theory you like. That argument is not from a traditional Astrologer, it's from Stephen Arroyo!!
There's an asteroid called Michael Palin (after the Monty Python star and now provider of many travelogues). I'm sure that one could make out a good case for asteroid Palin being important in affairs to do with long distance travel or being Very Silly. Statistics don't show meaning they only show association.
Throughout the Tradition the emphasis was on light and it's transmission and reflection - nothing happens without 'light' but this is not just the 'light' of scientific wavelengths it is the light of the 'soul' for want of a better word.
To end on a pessimistic note, unlike Dave I don't see any Human evolution over the last 100 years, or even over the last 2,500. Yes life is more complex technologically, but Modern Man is, if anything more capable of acts of gross evil, than Babylonian Man. I desparately wish it wasn't so. Beliefs in Mankind's progress to a New Age ignore what mankind is doing now and has been doing for quite some time. Do we need the outer Planets and the other bodies? That's for you to decide as you work through your studies.