Since USA units are so expensive, it is worth investing into healers early into the game, especially if you plan to turtle and boom. Every unit that gets back to full health is resources you’d otherwise divert from your boom.
I find 12/10 age up with French immigrants into Irish immigrant at 5 minutes it is the best opening so far. There’s also an age2 county that gives you a 3 pilgrim shipment, which are worth slightly more than 3 villagers. There are ways to greedy boom, but very difficult to survive early game if someone is determined to mess up with you.
China, Inca, Spain are very hard match ups for USA.
I typically use spanish in most decks along with french, dutch and irish. Only time I do not have spanish is if i’m doing a straight marine ff or something as the cards so valuable at just 300 food for an outpost, permanent xp trickle worth 1.4 tp’s and ability to call the pikes. I don’t just use it against aggressive civs.
Same thing applies vs a lot of civs, take portugal for example when they go 10/10 and ATP, you’ll need unit shipments and crates to get enough military out early and contest the tp’s otherwise you lose, 5 pikes won’t be enough vs ATP’s. Typically I don’t want to ship 700 wood just to make pikes and ship 8 crossbow but if I leave the tp’s I’ve lost. in many match ups like vs an aztec/russia rush unfortunately I just can’t send the bank as USA or ship 4 vills as japan, build all 13 kanchas as inca, max manors as brit etc. Match up will often force you to send a certain card that you prefer not to send or change your play style.