Well at first I may reassure you that your Neptune is not in its fall. There is no agreement among modern astrologers what the signs where Neptune and Pluto are exalted/in fall are. On the other hand, some astrologers believe that the outer planets Uranus, Neptune and Pluto don’t have any essential dignities in any signs. I can’t call myself much of an astrologer, but I absolutely agree with this opinion. The outer planets move too slowly to be pigeonholed into the concept of planetary dignities/debilities. In other words, their positions in signs aren’t very relevant for a particular person. What is relevant though is the aspects they make and the houses they are in. Following this logic, I can say that your Uranus is not dignified by its sign placement.
Now answering your questions:
1. Yes, of course, the planets that are in fall and in detriment in your chart are important and should be taken into consideration because they shape you as a human being. But it’s important to remember that this doesn’t make you any worse of a person. In fact, even planets in their dignities don’t always function for the best of an individual. For example, Mars in Aries is a great position for your Mars, it will make you very active, courageous and fearless, but if it is badly aspected or has some other debilities, the person with this position can become self-destructive and downright aggressive. The planetary debilities show that it’s hard for the person to make much use of these positions and it requires much time and work to turn them into something benefic. It will be up to the person whether overcoming these hardships is worth the efforts or not. You can live happily even without being perfect! In fact, no one is perfect.
2. I will very quickly analyze what these positions of yours could mean, but these descriptions are rather shallow. Sun in Libra will make your sense of identity incomplete, you can never push yourself hard enough to accomplish all your goals and plans because of your desire to always be fair and just, you may suffer from problems with your self-esteem. Venus in Scorpio will make you quite obsessive in matters related to love, you may want complete dominance over your partner which will make most people feel suffocated over some time, also you’re not afraid of using manipulation; if someone turns down your love, you can be quite vindictive and, while not necessarily, sexually you can be turned on by things most other people would consider gruesome and be into some kinks. Jupiter in Virgo can make you rather narrow-minded and unable to accept other people’s positions, you may feel scared to develop spiritually and learn anything outside of your routine; you may be afraid of trying anything new even if it can be exciting for you in the end and prefer your life to always head forwards on thin railways where you can’t lean left or right. Saturn in Cancer will give you a rather shallow understanding of the concept of rules and regulations, you want to be careless and free of all your duties and responsibilities because they make you upset and unnerved; you may not work well under pressure and very often you don’t seem to realize the simple truth: if you must do something, you indeed must do it, you can’t leave at any time you want.
3. The number is not really the issue, you still have to deal with any planet individually. The positions of planets in signs make up your personality so you can’t change the main core of it but you can make the best use of them if you cut down their negative expression. Don’t think of yourself as of being doomed or cursed by the Universe, there are a lot of people that have achieved great results even with not so promising charts. Like, have you seen Charles Darwin’s chart? If you haven’t, you should.
4. Well, of course, a planet in domicile is at home, it’s exactly where it wants to be and where it should be. For people with a planet in domicile its qualities come easily and are especially potent, but it depends on the person if he will waste their positive expression or use it wisely and responsibly. With great power comes great responsibility!
Finally, the concept of domiciles/exaltations/detriments/falls is not the end. For example, you should not forget about reception. Reception means that two planets form an aspect and each of the two planets is “visiting” the other planet’s sign. Say, you have your Mercury in Aquarius and your Saturn in Gemini. They form a trine with each other. While neither of them are in domicile or exalted, together they form a “bond” which is extremely beneficial for both of them because Mercury is in domicile in Gemini and Saturn is in domicile in Aquarius. This way, working cooperatively, they can achieve great results. When both planets win from reception, it’s called mutual reception. Mutual reception can exist when there is a square or an opposition involved, this way it doesn’t particularly make matters good per se, but the conflict between the planets is a lot less troublesome.
Also in traditional astrology there were some other dignities which are mainly omitted by modern astrologers, like triplicity, term and face. Those dignities are much weaker but still deliver some good effects. The planet not having any dignity traditionally was classified as peregrine. It wasn’t seen as bad as detriment or fall, but it was somewhat close. You can read about it here:
https://books.google.com/books?id=Z...q=introduction to essential dignities&f=false
And as a final point, there is another thing in astrology called as sect. It means that there are some planets which will influence you throughout your life more than the others depending on whether you were born at day or at night. If your Sun is above the horizon (houses 7-12), you were born at day, if your Sun is below the horizon (houses 1-6), you were born at night. The Sun, Jupiter and Saturn are said to be the diurnal planets, while the Moon, Venus and Mars are said to be the nocturnal ones. Mercury doesn’t strictly fall into neither of these categories, but is diurnal when oriental of the Sun (rises and sets before the Sun) and nocturnal when occidental of the Sun (rises and sets after the Sun). It’s also the concept of the traditional astrology. So in your case if you were born at day, you can expect somewhat less problems from your Sun, Jupiter and Saturn and if your were born at night, your Venus will be less problematic.