I think it's a good idea and I've done just that several times.
1. Yes you can use Photoshop, it's the best tool for it actually. You need to know your distances, correct: Start by deciding the square dimensions, say: 1500 meters. You may also want to draw a grid in 10 or 20 meter increments that you can overlay over your design, so that you can actually see the scale. I also construct a 600yd 2D-tape measure (=540 meters), that I use to map out my individual holes.
Anyway, when you make a new terrain in Unity, go to top menu, then "Set Resolution" and type in the same dimensions you used in Photoshop. That way, a yard here will translate into a yard there.
1b. After adding greens, fairways, first cut and bunkers, I also like to mark tees and greens with strong colors (this will help in Unity) and to draw a circle around the projected landing area of the drives.
2. Correct, the hole would go uphill, black is low and white is high. Don't fret about too much height detail, you can use the Unity tools for the fine tuning, just make sure that your general elevation changes are as planned: High, low, side slope over one hole and over the hole course. When you are done, slap a heavy Gaussian blut over your heightmap, to avoid getting jagged edges in the end (75 pixels plus)
Also, don't be too concerned about making it too steep or too flat, you can adjust and fiddle with the terrain height at import.
3. From the same Photoshop master file, make the following two versions:
- A jpg high res to use as your terrain texture to show you your layout in Unity (I usually make it twice as large in pixels as the terrain is in meters - 3000 pixels for 1500 meters)
- A "Photoshop Raw" file with the heightmap. This file is best sized 4096x4096pixels (Unity Maximum offering you most control over everything later). It also must be in the "grayscale" color mode and in 32bit. And, as the tut videos told you, it needs to be flipped vertically.
Then proceed like Mike did in the setup videos with the downloaded files. Enjoy!
Here's how it looks in action. To see proportions at all times, I like to plant a few person-cutouts into my scene, to check on sizes. I use Tara King for that (and if you don't know who she is, never mind...)
[attachment=67:tarafication.jpg]