its really just a matter of experience, being able to test water, do water changes, proper feeding etc etc.. just stuff that comes with experience, im sure that nancy will agree as her octo tank was her first, but she is also testament that it can be done!
Yes, Ollie was my first octopus. I prepared for some time before getting a tank, and followed all of Colin's advice. My tank was set up and running for four months before I got Ollie, and I would recommend this for everyone. This is not a thing to hurry into. I learned a lot during this period that helped me give Ollie a good life.
Keeping an octopus was a lot of work, expensive (to give her the best food including live food), time-consuming, and more stressful than I anticipated - but also more rewarding.