[Ragnarok]

1. Is it enough to have one weapon platform containing combat sensor and ecm (do they count as stack)?

If I recall correctly yes they do stack. So if you have say 10 WP on a planet but only one has ECM and Combat Sensor then the rest of the platforms will reap the benifits.

2. Is it worth to put ecm, stealth armor and scattering armor to weapon platform when there is -200% defence bonus by planet?

Dunno, I'll let someone else answer that one.

3. Is multiplex tracking needed in weapon platforms (I recall someting that planets can automatically shoot 10 targets)?

Hmmm, I don't remember hearing that before. It could be the case though. I'll run a couple test to find out. I'll get back to you on that unless someone beats me to it.

4. Am I right that the weakest cargo is destroyed first (usually mines first, then troops, satellites, weapon platforms) thus it's not reasonable to put decoy weapon platforms containing only armor/shields.

If you mean cargo as in the units are still on the planet, then the first thing put into the cargohold on the planet will be destroyed first IIRC.

5. What is the order how the mines are swept/exploded? Is it first-layed first-swept?

Yup, first-layed first-swept.

6. What is the order how satellites are destroyed? First-layed first-destroyed or weakest first?

Same as mines IIRC.

7. Is shields in fighter/satellite count as hitpoints or as shield? So how shield depleter and phased-polaron beam works against them?

I believe on units shields are just counted as hit points. Nothing more.

8. Is there any way to tell ships not to clear orders when go through damaging warp point? It's very annoying when there is black hole on the other side of the warp point and the warp point is two squares away from black hole... You can guess what happens, it's impossible to go through that system.

I don't know for sure. Someone else can answer that one for you.

9. How the race trait happiness actually works? If I have 20% happiness bonus is my natural decrease -20 * 1,2 = -24?

I know nothing about happiness and it's factors.

Hope those answer help you. And I hope I got most of them right.