It is completely intentional that the Father is the only one of the three Force-wielders that vanishes upon his death as Obi-Wan and Yoda do.
The lava used in the Well of the Dark Side uses some of the same elements from Revenge of the Sith Mustafar scenes, according to effects supervisor Joel Aron.
The very portable Jedi jumpseeders are based off a speeder bike concept drawings from Return of the Jedi.
Some of the concept design for the Well of the Dark Side was taken from early Ralph McQuarrie designs for subterranean levels of the Imperial Palace where Luke was going to face the Emperor deep within Coruscant in Return of the Jedi
Ahsoka is wearing a re-purposed pair of Hondo Ohnaka's pirate goggles with the strap removed.
Hidden among the constellations etched into in the Father's monastery is a wolf.
