Preparing Octopus.
 

I was just wondering how I would go about doing this (as well as cooking it). Both for topping things like nigiri and for takoyaki. Also does it really matter what size the octopus is? Thanks in advance for any help.

most octupos (for sushi) is typically first boiled (probably w/ a bit of salt) then frozen and shipped.
if, however, you do manage to get it raw, cooking it for too long will cause the meat to become rubbery. I've never prepared octopus before, so i can't give you any guidelines as to how to cook it.
as for what parts of the octopus is used...
typically, you cut the head off, remove the beak, and use the tentacles
as for the head
you slice it down one side to open it up, remove the innards, and the filament that's on the inside of the meat. to prepare it, i believe you first rub it down w/ salt then rinse it off.

for the tentacles, for sushi, you typically slice it (starting from the base; part closest to the head) in a diagonal. the meat is chewy, so you might want to tenderise it by pounding it w/ the hilt of your knife.

for the head, you can grill it and glaze it w/ a soy based sauce (soy sauce, mirin, sake, and sugar)

octopus goes great w/ lemon juice and that soy based sauce (head and tentacles)


as for takoyaki...
take the ends of the tentacle, chop it up and mix it w/ whatever your takoyaki recipe calls for

my experience w/ tako (octopus) is rather limited, but i hope that helps

Are there any guidlines for boiling fresh octopus?

You don`t just boil it in salt. You have to rub enough salt on the outside to remove the slimy coating before you boil. So you rub it down in salt, basically scrubbing it. Rinse, and if there is still a slimy feel to it - repeat as many times as necessary.

Once all the coating is gone, stick it in a big pot of boiling water. Watch it until it stops curling, then count to 30 (usually around 5 minutes, but differs with size) - then turn the heat off and let it sit for about 3 minutes.

We usually steam ours though, it preserves the flavor better in my opinion. But unless you have a good steamer that lets you dangle the octopus, it might be hard to do.

and that is my lesson for today >.>''
i learned something new~

danke nyo~ ^_^