Are you in a very space constrained environment? 5Gb isn't that big.
If you are space constrained, it's better to try and take lots of smaller extents unless your Dataclases (if applicable to your file) provide Space Constraint Relief which will split the allocation down to fit what's available to a point. Suggest talking to your Storge Admin people on that, and also ask if there is a Dataclas to provide Extended Format (EF) so you can have up to 123 extents per volumes and more than 65k tracks per volume, and this might also be a good candidate for Compaction.
Providing the VOL=(,,,25) means you can have up to 25 total volumes added if necessary with either 15 or 123 extents (EF) per volume. Volume count maximum is 59 for DASD datasets regardless of format.
You can also ask for space in numbers of records if you know that value.
SPACE=(80,(100,10),RLSE),AVGREC=K asks for space to cater for ~100,000 x 80 bytes records Primary and 10,000 Secondary for example.