You can have as many pacts as you want now, but as listed elsewhere, duplicate pacts don't stack.
With a given partner, you currently CAN have all the pacts active. So if you both have 200% against each other, and are at the top of the diplomacy tree, you could have all your pacts and all their pacts (if they are a different race) active.
Military strength is when you are too weak. If your fleet is stronger than their fleet, they get intimidated by you, and are more willing to listen to diplomacy instead of just smashing you.
I haven't figured out diplomatic inclination yet, but it thus far has remained constant.
The envoy cruiser 'temporary boosts' near as I can tell only factor into the 'envoy bonus' category (or maybe it is broken for vasari if you're seeing something else as a TEC?). This means that if your envoy has already worked up to the max (+1.5 per envoy, at least for Vasari, I haven't tried the others yet) then the 'bonus' won't actually show up.
One thing that I didn't clue into right away, is that EACH envoy cruiser can add an envoy bonus. When I noticed the AI just sitting envoy cruisers in each of my wells, I thought it was an AI bug that was just happy with the new shiny tools... until I realized it had a WAY higher percentage against me than I did against them. I tried the same strategy, and suddenly I was easily getting the 100+% needed for pacts, whereas without this tactic, I was floating in the 80-100% range only. If you want pacts, you need 1 fleet-upgrade worth of diplomatic ships out there gravity well sitting, and you'll easily make it. Just get that cease fire pact first.
