Sorry for the late reply, I dont log on here too much.
There are different ways to braid your hair to make it shorter on the dread, but as long as your hair is it will still go down the length of the dreads quite a bit. If you do not like to see the crisscrossing down the entire length of the dreads, then I would say your hair is too long.
Otherwise unless you get dreads that are shorter than your hair, your length should be ok. It will probably be pretty heavy given how long your dreads will have to be.
Another option is to get falls. They'll still have to be lengthy [and numerous and/or thick for good coverage], but you can put your hair into buns and take them out easier. That way if the weight is bothersome you wont have to spend hours taking the dreads out.
Hope I was of some help!