CHEMISTRY:
CHEMISTRY rarely needs actual parts, only chemicals. Duh. If you have substances you can mix and tubes to mix them in, you can perform CHEMISTRY. The gear you need as your level increases tends to be simple, relatively cheap things like titration equipment and centrifuges. While you'll soon need a dedicated lab for CHEMISTRY, it's easy and low-cost. In fact, the only real noticeable weakness of CHEMISTRY is that the costs of CHEMICALS raises over time, selling your wares to governments can make them more familiar with you (if that isn't what you want), and that you can and will be taken down if you try to become a drug lord without a lot of defenses and preparations.
The advantages are enormous. CHEMISTRY can produce superior batteries, reactors/engines, bullets (with a little PHYSICS anyway, but you start with an automatic level 1 in that [if you main PHYSICS the free level 1 switches to CHEMISTRY]), explosives, and missiles, as well as flamethrowers, chemical agents, and various drugs. With higher-level CHEMISTRY, you can make very powerful drugs (performance enhancement agents and otherwise), some of which world governments will buy wholesale. You also gain awareness of the side effects of taking multiple drugs/performance enhancers simultaneously, and can produce buffers, which can prevent low-level side effect interactions. In fact, the level 2 and level 3 performance enhancers with a buffer would likely be enough to get you through your first several encounters alone.
CHEMISTRY is not visually impressive at first, but rapidly gains as you produce explosives and chemical agents. Oh, and flamethrowers. And missiles. CHEMISTRY actually is needed for the biggest and baddest weapons around.
Sean: Nanobots are high-level (7 and up) KILLBOTICS that require high-level (also 7 and up) programming and a workshop tooled for nanotech/picotech.
Nuke: As your KILLBOTICS level raises, you can produce better robots from raw materials and even better ones with specialized parts, as well as making those parts yourself. Typically you're going to be able to make parts a level behind what you can utilize in an ideal robot for your level. However, at level 10 (maxed out) you become able to produce any part you need by yourself. You could spend four hours in a city dump and come rampaging out on a smelly engine of annihilation.
BIO and PROGRAMMING next.