#1
Would I have to change the nut at all it I wanted to chage the strings on my 5 string from BEAD to EADGC? Would they rattle around in the slightly large spaces or will it be allright as it is?
#2
I don't think you HAVE to. I'm not sure if it would effect the tuning or anything but I don;t see anything wrong with the idea.
My Bass Rig (Since Everyone does this)
Fender Jazz 5 String
4x10 Hartke Transporter Series
Behringer BX4500H Ultrabass Bass Head (Changing to a Hartke 5500)

My Band: http://www.myspace.com/morningnj
#4
I think you should change it. Even a small difference in size will make it rattle, and that's not a sound you want to hear. Always use the right part for the job.