I also set my cache-size=0 in /etc/pihole/01-pihole.conf. I have unbound on the same system, unbound caches, no need to have pihole-FTL do the same. As @wuast94 mentioned, the dnsmasq manual indicates this is a valid configuration:
-c, --cache-size=<cachesize>
Set the size of dnsmasq's cache. The default is 150 names. Setting the cache size to zero disables caching. Note: huge cache size impacts performance.
I have been running this for a while now, ever since the discussion about proxy-dnssec, never had any problems with pihole-FTL.
Only since the latest release of pihole-FTL (today - , FTL version is vDev-fb01e09), I've experienced crashes, see here and here.