Antenna Height

Whatever it takes to get a line-of-sight towards the towers. I'm not a big fan of EMT (1/16" wall) but it is better than the 16ga tubes that they sell on eBay.

Make sure you don't crush the tubing as it will weaken it significantly.

I think you'd be surprised what kind of a wind catcher those oven racks are.

1" EMT has an even thinner wall than 1-1/4" EMT. 1" EMT is only 3/64" wall and 1.163" OD. It isn't nearly as resistant to twisting as 1-1/4" at 1.510". You don't want the antenna doing a "parade wave" in a good breeze.

Technically you don't need to be able to see the lights on the towers, but even leaves will negatively impact UHF. The clearer the shot you have, the less you're going to have to worry.

As jimmy57 points out, you need to consider whether the antenna is going to perform well (or whether it even matters) for your PBS station being at VHF 9.

Telescoping masts often don't work all that well with guy-wires unless you freeze the sections. Depending on where you attach the wires, it may just work the mast down and allow it to tilt. It is probably best to have some sort of solid base and skip the wires.

I'm not convinced that it is reasonable to assume that a bowtie array is necessarily going to create less of a wind load than a Yagi-Uda. Wind is all about cross section, not weight or depth.

Understand that many of the theories I've presented are not the result of exhaustive testing but based in rudimentary aerodynamic theory.