How much gb's of space have you used for your samples drive?

Well my samples drive does not exist. But it should be pretty easy to calculate how much you will need. When you buy samples the sample-sellers usually make a point of telling you how very humongous they are, including pretty accurate GB counts. If you are concerned about the cost of storage, you are probably not going be able to afford too many TB of samples. If you are doing your own sampling, then time will limit your storage needs. 

Your projects size is a lot more difficult to estimate. Your time again is the limiting factor.

I have two ssd drives for my samples, a 64 gig and a 128 gig.  There's 27 gigs left over on one drive and 42 gigs on the other.  They recommend to keep at least 15% of free space on a drive for optimal performance.

It's working perfect for my needs.

It really all depends on what each person is seeking to do.

Someone who mainly records and uses very few VST's will have very modest needs in terms of storage for samples. 

OTOH, someone who composes in MIDI with high end orchestral samples from VSL, EWQL, and the like will need significant storage for samples, and the needed storage could exceed the recording drive.

Hard drives are like trash cans.  The bigger they are the more garbage you can accumulate between each empty out cycle.

My samples drive tends to be much bigger than my projects drive simply because I tend to archive projects away from my active drives so I use up any free space on my projects drive for additional miscellaneous storage as well because my samples drive ends up being full to overflowing.

If I ditched what I didn't use I'd probably have plenty of space but I always think my Bulgarian nose flute sample collections and such like will somehow come in handy one day.

My samples drive is 416Gb full out of 1Tb