Alex,
I flew on a 777 back in 1995 when they had only been flying for a month!! It was a lovely plane from United Airlines had all the extras such as seatback TV's etc and was configured as 2-4-2 as I remember, although this may vary airline to airline if possible?? Anyway you should have no worries travelling on one. Although it was strange seeing a wide bodied jet with only two engines, apparently the chance of one going wrong is very very very low. On that note I shall say enjoy your flight and holiday, you will love WDW and America.
By the way how is the visa situation??
Claire