try getting a prelightner then dying your hair - the swarzkopf prelightener is good, and then try using the Loreal hair kit things that come in a red box, you dye it an all over colour then you put highlights in - might need some help though can be a bit tricky on your own.
dont worry about how long you have to wait to put streaks in, i dye my hair all the time, last time i did brown with blonde streaks in i used the loreal pack then i got a superdrugs own highlight kit to add some more.
shouldnt be a problem that your hair is really dark, just try prelighten it before hand. i had purple hair before i dyed it brown!
hope this helps x