I do primarily drywall work and what I like to use when estimating a job is a simple worksheet.For example I list it like this
8'- III(3)
9'- II(2)
10'- IIII(4)you get the drift...
Use the longest size possible to minimize joints.
When your estimating a job-
1rst- find out local codes as to what thickness/rating you need.
2nd How are you going to apply it-standing up(eliminates butt joints,which are more difficult to tape)or railroading it(horizontal-minimizes linear feet of taping but now you have butt joints,most houses are hung the latter)
3rd Use the longest size drywall possible,it may be easier to transport 8' sheets but you will have more butt joints.
4.As far as mud figure 200 linear feet for every 5 gallon bucket.
5.Tape-just calculate the linear feet of your joints.
6.Corner bead-for finish closets buy 6'8 bead-requires no cutting and just buy whatever length bead to match your ceiling height(i.e. 8' 10')