I'm not a code expert or electrician, so take my suggestion with a grain of salt.
I think you could run 8/3 wet rated wire for now (or maybe even 6/3), and wire it as a 20 amp MWBC with a GFCI on each circuit. This means there would be no subpanel, just a 3 wire circuit for the garage. As an MWBC, it would only provide two 120 volt circuits and there would be no 240 volt circuit.
I believe the MWBC meets code requirements for a single circuit feed to a detached building. The only catch is that with larger wire I'm not sure a GFCI or other initial 20 amp device could accomodate the 8 gauge wire.
Later on you could upgrade it to a subpanel and add ground rods and other items needed to be code compliant for a subpanel that has provides 120 volt and 240 volt circuits.
Bruce