What database? Oracle? MS SQL? DB2?
Afaik, Automic does not specify a size for the tablespaces. Again, the more, the better. This page claims that 1 GB and 512M is barely dimensioned for a testing system, so you probably want more. How much more depends on your expected usage. The sizing guidelines say 512 GB to 2 TB for the DB, I personally think that's a bit excessive, but that is probably as close to an official recommendation as it gets. Most of that will be for UC4_DATA, with a fraction for UC4_INDEX.
Since you said in another thread that you already have a 12.1 production system, maybe some guideline on required storage can also be taken from there? Also, if your chosen DB system lets you expand table spaces later, you can always expand (though possibly with a downtime).
Hth,