I would do it at 500-600. Don't put it too high if you're still wanting to grow your infrastructure. 800 isn't too high, though, if you want it there. But during your first few wars you will weed out the bad apples.
We only have three requirements in Invictus Army. Be active in donations(sending and/or receiving) is one of them. We don't care if you get 500 and send none or send 500 and get none. It shows you are actively attacking or contributing. The other is communicate. You don't have to talk every 5 minutes, but communicate when you're attacking or afterwards if there was an issue, or where traps were that set you off track. The third requirement is that IF you opt in to war(it isn't necessary), that you use both attacks. We understand there are glitches still with the game, but we can tell when there are some(If you count the total attacks used in your alliance's battle report then refer to the battle report for comparison it will tell you 2 or 3 or 10 crashes happened). If you fail to make one and you are a solid contributor, had justifiable reasoning or it had no effect on the result you get a pass, really. If you fail to make 2 we sit you the next war. We include you again in the following war and if you fail to make any attacks again, you get DAS BOOT(booted). That sums it up for us. There are other Alliances that use similar tactics or none at all with it and only boot inactive people when they need the room.
I think you guys will be just fine. Your BIGS will be able to carry you through most wars, so I suggest starting with a 15V15 at least. That basically guarantees you get 14 bases 5 starred, providing you use good tactics. I don't mind discussing tactics with you as far as WAR goes, but I would prefer to do it via private message. I'm sure you can and will come up with your own, but the offer is out there. I wouldn't mind picking your brain, either, for opinions.
Good luck out there.
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Invictus Army!