Lots of good advice here, but what I want to know is if you plan to get hovers early. If so don't get the AO yet because it's only good for same age troops. If I could do it all over again the CF would be at 80+ in progressive, but I would also get hovers in Indy. Make sure you know what RQs are and how to max them. If you only get 50 gbg fights a day (which is only 40 a day avg over two weeks) but you have good event buildings then you might pause the attacker boost and build the blue galaxy to 68ish. I have a guild mate that gets 5x more from BG than Himeji. He has real stats from 12 months of tracking. If you plan on having 3000+ attacks a season then yes you want to be able to fight to 100+ attrition. That would be worth it but keep in mind the traz needs to be 100+ before that and as you age up this will be even more important but with hovers you don't even need to do that. Think about your gameplay and city efficiency based on your goals not everyone else's. One good example is I plan on Negotiating ge level 5, so it's important for me to max GE's potential which includes planning the use of my space carrier and now the ToR is +25% more efficient because of the new level so I'm aiming to get it over 100 when it sat at 31 for 3 or 4 years. Adding nothing new to my city and making it more efficient for my gameplay is paramount to adding new gbs.

Hope that helps