Darth Lefty 

I'm looking at using Zwift and trying to figure out all the things that I need.

I had a shopping list here when I started writing but it was getting to be a mess. So let me just ask, what do I need? Right now I don't have a trainer, smart, dumb or otherwise, and none of my bikes have any sensors. So it could go a lot of different directions and I don't think there's some optimum minimum amount of stuff I can buy. For instance I can think of a lot of scenarios where sensors could go either on the bike or the trainer, depending how smart the trainer is.

I have, bikes: a single speed gravel bike that could be set up 1x11, but limited to 38t front, and might bear mentioning a 73mm bottom bracket shell, and a thru axle; an old steel 14-speed racing bike with pretty tall and narrow gearing; an even older but very nice for its era 10-speed with even more limited gearing. Electronics: a Windows 10 laptop; a Roku TV; an iPhone and Apple Watch; a fan.

I have at least figured out that I can get Zwift to talk through the phone to the HRM on the watch, and I'm guessing that means the phone is the head unit for all the other sensors too.

Can you do smart bike / dumb trainer where you wire up your bike completely with power and speed and cadence? (I wouldn't mind having an excuse to buy a Stages XT crank arm.) But then you need a speed sensor too? because no GPS

Clearly you can do a dumb bike / smart trainer, but then what is still missing?

What kind of gear range bike do you need? Same as you would want on the road? Clearly I've made some really limiting choices in my bike acquisitions...