TAZ from what I can see this is your first fish; up to you of course but I would reconsider going for a 12" or 18" monster fish for your first fish (let alone one that could take off your finger).
As a new hobbyist, despite all the questions being asked now, you still WILL make mistakes, and fish will likely be lost due to these mistakes -- we've all been there, it's a natural part of the hobby, learning and growing from our mistakes. The question is do you want to go through this process with a larger, more expensive fish you're emotionally connected to already it seems? IMO it would be better to learn the ropes with some smaller easier fish, then progress to something bigger, more expensive when you have the basics down, just my 2 cents, best of luck whichever way you go.