To answer the original question, the best place to locate a fuse is on the positive lead as soon after the battery pack as reasonable, preferably at the battery post. As stated earlier, the main purpose of a fuse on the battery power supply is to prevent fire or battery destruction in the event of a short circuit, not to prevent circuit failure from over use.
As to what size of fuse to use. A 700 Watt motor at 36 Volts can use 19.44 Amps of current plus the controller circuitry will also use some current as well. Fuses should be sized at 125% of current demand so a 25 Amp fuse would be about the smallest size you should use unless you want to be stranded when under a heavy use, I think your 30 Amp fuse is about right.
Dale