There are several things in your post to address and I'll try the best I can to do so in order.
-Although you are right, to a certain extent, try not to pick out any planet and single it out as most telling. What I mean is that the nodes are like rowdy children. Rahu in its obsession and outward nature and Ketu through its withdrawl and inward nature. However, the other planets give the strengths and weakness to support them, or not. We don't use a hammer for every job that comes our way, right? Well, some of us do, but that's how we get into trouble. Little nit picky but I hope that came across well.
-Every planet is a karmic planet. Your whole karmic map is expressed through the 9 grahas. Sun in your steadfastness and courage. Moon in your capacity to have a still mind, feel secure, and express and feel sattvic love. On and on, right?
-Given this, the karmic lesson you must learn is the expression of all of your grahas where ever they are in the order of the dasa system. Yes, you will learn lessons of all of the grahas outside of the dasa system but the largest of the lessons will be learned through the dasa cycles. However, I will say that the nodal house axis will pry for your attention more than the others, only because that is the nature of the nodes.
-The thing that will interfere with marriage, as well as other personal relationships, is the venus/rahu conjunction. Over indulgence being the key here. I see this as more of a potential to hinder you more than your potential partners. I say this because it will be your excitable desires that won't feel satiated. This can turn devotional if you put in the work to withdraw from over stimulation. The search for love is a result of our individual consciousness and not so much because of this or that graha. We are constantly swimming and a vast sea of love and are blind to it and we go and try to find it from an equally blind other
! However, I will say that your search for a partner will feel obsessive because of this combination.
-The house system used in vedic astrology, popularly, is whole sign, I believe. Each house starts at 0 degrees of a sign and ends at 30 degrees of the same.
-In regard to Ketu, one must remember what the nature of Ketu is. Ketu is the renunciate. The final liberator. It makes sense that these transits would show losses and such sufferings. You have to remember that this world isn't permanent and Ketu, along with Saturn, want nothing more than for you to see that. Give some focus to Ketu, find your inner connection with divinity because that is what the drive here is for.
Hope this helps!
