Connect null-modem serial cable, configure your terminal as 9600, 8 bit, no parity, switch FAS2040 - it should attempt to boot. If it does attempt to boot, you can then initialize disks; depending on version currently installed you may need to have full operating system archive. It could be a challenge to work with it if you do not have access to NetApp support site downloads ...
How can I obtain license codes for ISCSI, nfs and so forth, for my second-hand NetApp FAS2040?
You have to ask original owner to give them. And I do not imply that you can legally use them even in this case ... IANAL.
When I install 3 disks and install Ontap 7.3.2 RC1, will it have licenses?
No. You will need to manually register them. And you will need original installation package of Data ONTAP to finalize creation of root volume, because some content is simply extracted from this package and is not present on boot medium.