If you can afford to, you always want to take +20% research and/or Technologists on Maso or higher-at a minimum the +20% research, but both is better. There's a hidden modifier to the player's research bonuses on difficulties higher than Tough, and Maso+ is where it really begins to show itself.
If you can't afford to, you really want to figure out how you can afford to.
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I would say you're probably colonizing too little...5 planets on a large/all abundant seems very low. Are you by chance rush buying your colony ships? If you are, don't do that. Medium and above, the only things you want to rush buy early are improvements so that you can afford to build ships.
Although it doesn't seem like it would work with your strategy, it's important to keep in mind that leaving an AI with one planet doesn't count as taking them out of the game for diplomacy purposes related to the other AIs, so as long as you don't go around instigating all of the wars, if you can leave an AI with a single planet (preferably surrounded by yours), the other AIs won't perceive you as a genocidal monster.
(I haven't played MV, hence the rather obvious lack of medals. But if you'll look around the forums, you'll see I know what I'm talking about.)