A console is a plastic housing used to hold an SPG plus computer and/or compass or all three. It is a 'console computer' only because of where it is. The same model can often be worn on the wrist, as can the compass module stuck in the console. (Usually as some do actually connect to the hose and serve as SPG as well.)
I'd urge a good look at a BP/W. Traditional BCs are a big expense and often do less well than a BP/W which is often much less, more rugged, and more adaptable to how you want to use it. Take a read through the threads here on them. The one linked above seems out of stock, so here is a different one, and they will thread the wedding for you, which is a bonus. DiveRite makes good stuff.
BP/W Package Configurator
You should be perfectly willing to use your octo the whole dive. Otherwise get a better one. Mostly, just get the same model for your primary and backup second stages, or just equal quality.
A back up computer is not the norm for recreational diving. In the unlikely event something goes wrong with it, you can just ascend slowly, ideally pause while you count out three minutes for a safety stop, and be fine, plus your buddy should have theirs, so they can help you on depth and timing. Tech divers need backups computers, but not so much recreational ones. Deep6Gear has a nice looking rec computer that is $255. There have been long discussions on it here. I would skip the whole console thing, just have the SPG there, and get the Deep6 plus a wrist compass. They have nice regs as well, though you typically have to mail them off for service. I have two of their regs.
A perfectly good SPG is this one:
DGX Thin SPG, Naked
DGX Black Face Premium SPG, Naked
Plus these have no logo cluttering up the display of your remaining gas! I find white on black easier to read than black on white. You need a hose as well, they have options for that also.
Almost all SPGs are made by the same company in Italy, which those are. I have the thin one as I dive sidemount and it is less negative so hangs better for that. But the heavier, and larger face, other two are more the norm for back mount, likely the 2". Deep6 has, extremely likely, the exact same SPG, just with an orange face.