For Flash & RAM available for Open AT apps, see Section 2.3. Open AT Framework Memory Resources in ADL Manual. RAM is dependent on your Open AT build setting. For Flash, there is a table added in ADL Manual v6.36 which is easier to comprehend.
For total Flash & RAM available on the module, see Section 4.9. Request identification information ATI in Firmware Manual. It can be read in the response of ATI9.