Engine tech is Gas Core Anti-matter (abreviated to GC-AM in the engine name). It's pretty high up in the tech tree, it costed me 975,000 research points to get the gas core power plant + engine tech. I have a crazy good research guy though. He is 60% bonus 40 research labs, produces 136,000 RPs a year. I started the game with him at 30 labs and 30% bonus and kept him researching engine tech 24/7. He grew in ability really quickly (I guess due to luck? seemed like every six months it said he improved something) and was 60% and 40 in like 3 years, so he was the key to advancing my engine tech. Even with him it took a good many years to research it though. He was also key in developing my jump engine tech, which is up to efficiency 16 now - letting my 20k ton jump ships jump with 6 other ships with only size 35 engines.
He recently developed a health condition though, I just put him on Plasma-core technology but he'll probably wind up dieing before it's finished - then I'll be stuck with the 20% bonus 15 lab limit PP guy that has never once improved even after researching like 50 things (missile engine tech, capacitors, all my designs, etc).
Micro:
You need active sensors on anything thats going to be fighting solo. If you're using them in a fleet with a sensor ship they don't need sensors, only fire controls. But if they are working solo they need actives to light up the targets, otherwise they can't shoot them. If you intend to use large groups of them, one option is to have most of them without sensors and just a few with sensors to light up targets. In that case you have to make sure they don't get destroyed first though, otherwise the rest of the ships won't be able to fight.