congradulations on your wakeboard boat. what kind did u get?
anyway...about rope length, you want to be somewhere between 55 and 75 depending on your riding ability. if your just starting to wakeboard, i'd say to start kinda short to get the hang of jumping wake to wake. if your experiended lengthen it to about 60-65. once you get really, really comfortable, you can make it even longer if you want. the longer it is, the more speed you can get cutting into the wake, and the further into the flats you will land. really, its all about preference, but thats the way it works.
now on boat speed, stay between 18 and 23 about. i prefer to ride at 19.5 because 18 feels to slow and if im going higher than 21, i feel like im flying. but thats just my preference. u might feel more comfortable going faster. kinda like with rope length, its all about preference.
i hope this helps