Scuka

Since I've installed some mods that add a bunch of new parts to the game, it became difficult to navigate the Parts menu when building rockets. Are there any mods out there which improve the user interface in VAB? Maybe something that will sort parts into smaller categories, add a search function etc.?

Yeah, it was the fuel imbalance. For some reason, I was absolutely certain that I connected the fuel lines correctly when I was trying it out. I was wrong, though xD

So, as you can see on the image, it's a pretty basic rocket. It's perfectly symetrical, all fuel tanks are 100% full and all engines are set to 100% thrust. yet the center of lift is shifted to the side, causing the rocket to have a tendency to tip to the side. Placing some winglets on the rocket fixes it. But I don't understand why it's shifted without the winglets and how are winglets putting it back into the center? None of my other similarly designed rockets have that problem.

Yeah, testing for take-off from Kerbal is fine, but I'd be a really unhappy person if I landed on some planet and then realised I don't have enough fuel to get back.

I belive those Delta-V maps are what I need. Thanks to both for your awesome answers.

Simple question, how do I know if my rocket has have enough fuel and engine power to reach orbit on a certain planet/moon? And in general, how do you know the amount of fuel you need to get from A to B with given weight and engines used?