technically speaking it's best to have for every 250k nw around 10% agents, 25k agents. once you hit 1 mil you should have 100k. Now, if it were me I'd have around 150k. But this is assuming you have the ideal empire, 100k wizzies, 100k agents, 200k ground and an appropriate amount of trannies, say 2000. That takes nearly 500k nw, leaving buildings at 500%? and pop plus research and planets. Ideally 100k but my opinion is 150k

now as to ops, if you're 6 mil and I'm 500k but I have a dozen planets and 400k agents and you have 400k agents, I'm going to succeed in all but Nukes. Nukes are tricky, they require luck more than any other op. I'd say I would still be able to nuke you though, maybe once, since you have such high nw. However, you nuking me wouldn't work because of the nw difference. The higher the nw FROM the enemy you are, you have less likely the chance to succeed and vice versa with lower nw, that way it balances the game out. However if you have 2.5 mil nw and I 2 mil, and you have 750k agents and I 600k, then you have probably about a 60% chance of nuking me compared to if you have 1 mill agents and I 600k, which would be about a 80% of nukes. (the percentages do not add in random fails)(also precentages are based upon my past experiences and eductated guesses) The idea again is that the more agents you have the more you are "Protected" and the more you can send out to nuke or w/e.

Let me explain the ops themselves, we actually discussed this somewhere once, but Easy ops have the best chance to succeed. You have 500k I have 350k, I'll be able to Spy you, might fail once. Infil, might fail a couple times because that's a "medium" op. Hard ops are usually the ops that do damage to an empire in a way that is viewed as an act of war. IE, nuking someone means "FU" or you're being an asshole and estorming someone's pop implies that you're killing their economy and most likely for a reason. However, wizard ops are harder to predict because of the magic bonus. Agent ops are easy to predict.

dumbed down it comes to this: There are easy, medium and hard ops. All ops are dependent on networth and # of agents. More agents you have than enemy means you are more able to do w/e to them. Equal amount means you need more nw (which is usually best but if you have much more nw than them, and equal agents, you'll fail quite a bit) and less agents depends on your nw and their nw. It's all listed out in the FAQ

Disclaimer, if something here doesn't make sense, it's because I have exams and have 0 sleep and can't think straight. I will revisit this later and revise if necessary