I've done it a few ways... The easiest is with a stop sleeve (need crimping tool) and stainless steel bolt & nut. Simply crimp the wire and insert bolt into joining plate. I no longer use "buttons" on top of the joining plates since the were decorative anyway and I've switched to a coated steel wire.
Just a heads up, this isn't a
DIY weekend warrior project. I usually get the tanks in rough shape, break them down, clean, measure cut, measure and cut again, drill, caulk, listen to wife complain there is no room in the garage etc. From start to finish it takes over a month sometimes two. In the end you can have a custom tank and save a couple grand if you don't mind the work. I've built one tank where it has a built in drain, turn a gate value and it drains 60g. in a few minutes making water changes a breeze. One of these days I'll add a build to my profile.
Good luck on your build and happy reefing.