How to set per user mail quota for postfix using policyd v2

It is possible in policyd v2 (cluebringer). You can define rules for each policy (1 policy for incoming email, another policy for outgoing, another for SASL). And then you can assign different policyd components (grelist, SPF, quota) to each policy.

http://wiki.policyd.org/documentation

You defined the policy check in smtpd_*_restrictions, therefore it will never be queried for mail generated locally, because this kind of mails is injected into the Postfix queue using the pickup(8) service. To circumvent this, you will need to modify master.cf and add a content_filter instance to the pickup(8) service (and of course, you will also need to add said content filtering instance, take a look at Content Filtering.

FWIW, I don't think it's worth the effort to do this. Nobody should be able to generate local mail on a mail gateway, and is not the central mail gateway, then you are limiting in the wrong place, anyways.