The damage up perks really depend on what weapon you are using. If the total shots to kill are not reduced then you will only see benefit from them in incredibly specific and rare situations. If it does reduce the shots to kill by even a single shot then it is probably worth it. You can test this with the weapon practice area and even see how it stacks up against people using 0, 1, 2, or 3 defense ups (you will probably see most opponents with 0 or 1 this early in the game so that is probably something to keep in mind).
The ink resistance is a very interesting one but also somewhat weapon dependent. If you are using something with great coverage directly around you like the jr, aerospray, or rollers the ink resistance probably won't play that big a role. If you are using weapons like the chargers, blaster, or generally weapons that are not as efficient at inking the immediate area around yourself it is a useful ability to have.
What abilities you choose to take really depend on what your personal play style is more than anything but even then there are certain situations where something just is not doing you any good like running a damage up on a roller where you will almost never see benefits from it.