Hello and welcome to r2r,hope all is well .
No experience with octopus so no advice to give you other than what I could read on Google then tell you myself ha ha.
Me personally from the very little research ( happenned to just read bit here and there on octopus is all) I wouldn't want to keep an octopus and especially if never had saltwater tanks before as I would want to have experience on keeping the apparently simpler things first before an octopus and be confident I could get to grips with all the testing of parameters ,salinity,temp and all the basic stuff first.
But if you go along with it, I wish you best off luck and if you not sure on set up and stuff like that,more research probably needed,all I know is apparently messy eaters,need tight lid as their middle name basically houdini, don't live to long in captivity,some octopuses like the very small blue ringed are extremely poisonous, then there's I think its called Atlantic octopus that grows absolutely massive.
And if memory serves me correct,they got multiply brains ,one in each tentacle/arm or something like this
But won't tell you that you shouldn't keep one as I say no experience on keeping one and not done the relative research for myself etc.
But sure there's lots off articles online if look for them and maybe even a few threads on r2r if use search option etc
Anyway welcome and good luck ^_^
