Ideal hilt length?

[darth_chasm]

You won't be able to stack your board and battery, so end to end they are going to eat up around 4 inches of your internal space. Then you have to consider the 3 resistors, wires, speaker, blade depth (typically 1.5-2"), heat sink, switch, recharge port and so on. I think you are going to find this a pretty difficult build. Space gets eaten up very quickly in standard size hilts. At 8.5" (theoretically 6.5" minus blade holder) 1" ID space will be gone in no time. Not discouraging you, just pointing out facts.

[DarthSkummelavsky]

I am with camp depends on the user and whether or not they want a one handed or two handed saber. For shotos and trainers 7 1/2 in to 9 in is good for most with 24in to 34in blades. My personal saber,OPPROR, is two handed and overall length is about 13.5in plus 40in blade. I am 6'1" tall, so the Shien/Djem So and Soresu styles better suit my stature.
My personal criteria for saber and blade length:
1. Saber fighting style (Shii-Cho, Niman, Jar'kia, Makashi, Soresu, juyo/vaapad, ataru and etc...) will determine whether or not the construction will be one or two handed
2. Saber wielders' height (very important consideration for overall blade length), think how silly Master Yoda would have looked fighting with a 42" blade.
3. sabers function (trainer, secondary weapon, ornate display or battle-tested companion)