After wasting 4+ days (I'm not even sure) I think I've managed to strip as much as I can and ended up with a minimal installation with (hopefully) great standby time (still testing) and even greater performance.
1- disabled as much service as possible, including:
-- afp: performance hog, smb3 works great with mac os.
-- nfs: never used
-- ftp: ssh already offers sftp
-- external usb: never used
-- logs: waste of memory, never checked before
-- winbind: I don't have any PCs
-- cron, media server, etc.
2- cleanup: removed some obvious useless files/folders. once you do it, it may take 10-20mins to reboot, don't worry and just wait for file system check to complete.
3- ramlog: dropped its size to 10M to prevent swapping.
-- applied msg.sock tmpfs fix, integrated to init.d samba file
-- disable spoolss: disables printer support: improves disk standby time
-- added streams_xattr: gets rid of dot underscore files, lightning fast directory listings, and drops cpu usage
-- increased deadtime: default is unlimited, improves disk standby time
-- disable netbios: disables nmbd which improves disk standby time
-- disabled log file: save memory to prevent swapping
-- added smb & removed afp: connect from sidebar
-– removed tally (/usr/local/bin/tally doesn’t even exists)
–- removed mediacrawler
-– removed individual share size calculations
–- disabled rotateLogs (run-parts /etc/nas/wakeup.d)
–- mount / noatime,nodiratime
–- decrease vm.swappiness
–- added afp fix (killall cnid_dbd) (if you decide to keep afp, this one prevents spin-ups)
–- added sleeptime logging (/var/log/monitorio.log)
–- added log truncation
-- decreased swappiness: keep it in memory
-- stop cron (a couple scripts restart it)
-- added debug mode: stop the service and run it from terminal to pinpoint processes that read/write
- no more 7 seconds sleeps
- stays asleep hours (hopefully will standby days)
- read/write speeds jumped from 55/40 to 100/85 (due to low cpu use)
Once again, thank you Bennor, rac8006, and Ralphael!