A Golden Age should allow you to bump your Gold Slider down a notch. With it breaking even at 30% IN a GA, then it was probably breaking even at 40% when the GA ended. And since you need lots of gold to get your units upgraded for a faster attack on your next target, you probably set it to 50% or higher.
As a short-term solution to get your units upgraded, that's okay, but as a long term solution, it will hurt your research (or espionage if you're going that route). Maybe I'm too much of a slave-driver when it comes to research - I like to be able to research things quickly - so I could be overreacting here.
I suppose upgrading your units isn't all that critical if you already have a tech+numbers advantage.
And I suppose that if you're able to get significant extra production out of stationing all those extra guys in your cities instead of using them to grab new lands, then that works too. I didn't pay close enough attention to see that, sorry. You're still early enough that you could get your caps bumped up later with trade, and maybe the extra military helps dissuade attackers, but I consider this a VERY short-term solution - you need happiness from somewhere else, and I usually get it from trade. All those guys WILL start to cost money, but at least you're not suffering from MY typical lack of force early on.
Did FDR have that whole side of the continent? I suppose I could call it a mistake not to have a Scout running around his lands, verifying his infrastructure all this time. If he did have it, it probably took you forever to conquer him, and you probably had to deal with WW while you did it, or hit him in chunks. Having Vassals on would likely have made him cry uncle after just a few cities had fallen, saving you all kinds of hassle (unless you wanted the whole continent to yourself). Even so, did the conquest feel like it was setting you back for a while, or did it go smoothly and the new lands got integrated quickly?