What would you recommend for me then...
Easiest possible solution for you is getting 4iiii on your praxis crank. $399 from 4iiii directly, although perhaps you can contact praxis to get a left crankarm pre installed (I'm assuming zayante is compatible with your crank). If your intent is to transfer to a new bike then as long as you move the whole crank or buy a second praxis crank then you'd be in good shape. I specifically bought stages originally because I had 4 bikes with shimano hollowtech cranks and swapping left crank arms was easy.
But as others have pointed out, getting a power2max is probably a better choice if you're going to end up moving the whole crank because it's only marginally more expensive and is a spider-based sensor. If you did go that route i would recommend against getting a true BB30 crank as it limits bb compatibility, especially if the frame you're thinking of getting is BB86. Same issue with chainring based powertap P1, which won't work with modern shimano cranks.
Pedals are an option as well, although I personally think they are overpriced compared to alternatives(799/1199 single/dual?) and require a torque wrench to install (garmin).
I personally don't like the powertap because of the weight penalty and it inherently means that you only collect data during training when you're not using your race wheels. It also ends up costing as much as the crank alternatives when considering the full cost of a wheel.
Because you don't have a coach and you're not a huge data nerd, i don't think you need to worry about the single/dual stuff these guys are obsessing about, stages/4iiii are fine.
So here are some options:
1. Get 4iiii installed on your praxis (399) and transfer to your new bike later
2. Get a 105/ultegra crankset with a compatible stages /4iiii crankarm ($600-800) and swap just the left crankarm with your new bike
3. Get a new power2max, pioneer, or quarq d-zero full crankset ($650-1000) and transfer to your new bike
4. Buy a pedal or hub based system.
Options 2 and 3 come with the benefit of potentially changing your gearing to something more appropriate for road riding.