I have ~40.000 pieces, mostly creators, lots of 90's system (quite a few BURPs and baseplates) and some custom bricklink orders. It's all stored in a 80cm X 150cm X 40cm space, inside boxes and zip bags...
No idea how to estimate better than that, but i'll give you an advise against sorting out by parts. My collection is sorted this way and it's a pain to find stuff, there are too many parts that don't have a clear category to be in.
I think the best way to go is:
-determine a few parts that have a clear category, like bricks, plates, technic connectors, and any kind of part that you have a lot. These parts you'll sort by part type.
-separate big parts, like BURPs and fuselages and put all together in a transparent box.
-the rest you sort by color... if in this stage you keep seeing the same part over and over again, put them in the 1st category.
-if you have lots of minifigs and minifigs acessories, separate them too