Civilian Oversight is a safe bet as a default occupation law, but there are some exceptions. As Germany, you can use Harsh Quotas in the lowlands, Denmark, and Norway if you plan on using the Reichskommissariats. The main benefit of civilian oversight is that it builds compliance faster than any other law, leading to more factories and/or resources in the long run, and eventually reduced resistance. (The secondary benefit of civilian oversight is that it also significantly reduces the required garrisons, thus ultimately rendering most occupation laws redundant.) The Reichskommissariats decisions can bypass the need for compliance entirely, and Harsh Quotas gets you more factories and reduced resistance in the short term. Generally speaking, the choice of occupation laws is much simpler than it appears. There are two extreme strategies to choose between, either Civilian Oversight for the long-term benefits, or Harsh Quotas for short-term ones. It behooves you to use one or the other as the strategic situation dictates. Wherever you had collaboration, use Civilian Oversight there. It also follows that, wherever compliance is good, collaboration operations are also good.
20 Cav+MP does get you the greatest benefit out of your MP company, but there are diminishing returns there. I've made the change from a 10 Cav+MP template to 20 before, and the benefit is not amazing. In the unmodified game, where this change costs you 50 XP, it's often not going to be worth it. Definitely push it up to be bigger than 4 Cav+MP, though; the benefits of going to a bigger template are fairly strong initially.
