Re: dhcp Maximum number of entries has been reached.
According to the Maximum Values Table, 200 is the max number of reserved IP and/or Mac addresses. This limit is hard coded into the fgt hardware. If you need to have a large number of reserved "static entries" you may be better off with running DHCP (service) off an internal server (which you already surmised). Alternately, as a workaround on the fgt you could pretty much set the lease time to unlimited, thus given each device a virtual "static IP".
NSE4/FMG-VM64/FortiAnalyzer-VM/5.2/5.4 (FWF40C/FW92D/FGT200B/FGT200D/FGT101E)/ FAP220B/221C