Keep forgetting to post and on mobile so here's the short story:
Ordered just the console paying all but $20ish with live money and $20 on an Amex. Purchase screen was correct. Next day, check shipping and notice Amex was billed full amount. Checked email receipt and it was the same. Amex site and ms balance confirmed it. Called ms and they couldnt change payment since it was processing. Recommended i call Amex to cancel, who can't cancel and thought it was odd ms suggested it. Hour later i get a shipment notification it entered shipping earlier in the day. Xbox arrives in 2 days and i call ms. Can't change payment type. Have to buy and return. He keeps trying to do the buy first and it won't work. Says return must be complete and then i can buy. Complete return and place order all with ms credit since i bought more to cover the total. Get an error that I've bought my limit. Call ms and they struggle to fix it. Say they will escalate it and call back within 3 days and don't place a new order. They call back in five days and it still won't work. Awaiting a one to three day call back for five days now.
This would be a LOT easier if they didn't shut down all the physical stores...
I've read too many horror stories about trying to do multiple payments to buy a console from MS's website. Definitely in the future, if anyone is close to covering the balance with your MS credit then go ahead and buy more MS credit to cover the remainder.