The main thing is to keep the order of operations right and remember that crimson amps etc. don't affect Invasion-Only bonuses (like when it says Invasion Attack +45)

My sheet has all my weapons listed separately, with attack and invasion attack in separate columns.

Add up all your weapon attack. Make sure to get every last thing that adds attack - it's easy to miss a couple mission items or Hull/Attack hybrids.
THEN add your Tactical officers to that. If you've done it right, you should match your 'Attack' stat in GL.

I made separate columns for each attack buff - so I could see my attack if I had just an obelisk and foci, or if I added an amp, and then a crux amp.

(((((Guns + Officers) * 1.05)*1.10)*1.15)*1.10) = Fully Buffed Attack (FBA)
1.05 = Foci 1.1 = Obelisk 1.15 = Amp 1.1 = Crux

Remember that buffs do not affect Invasion Attack, so do not factor it in at this stage!

To calculate your invasion attack bonus, separately add up the Invasion bonus from items like the Psi Emitter and Prototype Mech.
Then, add it on to your earlier figure:

(FBA + Invasion Attack)

If you have Atmospheric Decimators, I'm told the 7% affects everything, as does the 20% if you're a Konqul. So the full thing you want is:

((((FBA + Invasion Attack)*1.07)*1.07)*1.2)

1.07 = Decimator 1.2 = Konqul-only bonus

Right, the the formula I gave doesn't tell you your chance of succeeding an attack, it just tells you what your total attack would be for the invasion, with everything factored in.

To see what defenses you'd have a 90% (max) chance against, do

((Total of Everything/3)/.9)

I remember reading someone, mento maybe, where they determined that buffs do affect invasion attack and invasion defense, maybe it was just invasion defense...?

My experience and spreadsheet do not support that. Legion bonus does apply to the invasion defense stat (Lazuli Pylon, Soldier Outpost, etc) however. Not sure about +xx% Defense buffs such as Barrier Nexus effect or even Xecti racial bonus though as I've not failed on any invasions with that category of bonus.

So you're saying a lazuli pylon with a barrier nexus would count as 600*1.3*legionbonus?

Sorry, I misread, I meant debuffs do effect them.

I had been seeing some discrepancies on my spreadsheet so it might be do to that. I wouldn't be surprised if they do. I'll have to check on the next one I invade (after I update it for all of the invasion items + %invasion bonuses there are now).

if a player is inactive, I hear tell you can have over an 90% chance of invade, but I've never been able to confirm this as you only see your chances on a failure...