I'm fairly new to this also, but I prefer hollow grinds for hunters and flat for kitchen cutlery. After looking at your picture a couple of thoughts came to mind. 1) a hollow grind works best if you keep the height of the grind line up from the edge at a height that is compatible with the width of the steel, the diameter of the wheel and your marked center-line. There's a widget on the forum somewhere that calculates that height for you. For example 1/4" steel with a 1/16" center-line has a grind height using a 10" wheel of about 1". A 6" wheel with thinner steel would be appreciably leess than an inch.
So, first step is to grind the blade steel at 45 degree angle on each edge with an old belt. The I start grinding up from the edge with a new belt, adding a little more pressure as the grind approaches the tip. This pressure creates a natural taper, and frankly is just happens as you try to bring the grind line to the center-line marked on the edge. After a number of passes you develop the "groove" for the wheel and once you get into that the grind is as much feel as sight. Slowly bring the grind line up with each pass measuring each for "equal-ness" of the height of the grind.
One other thing I learned, never quit on a grind line. Always keep suitable pressure from ricaso to tip, and that means doing something to protect your fingers 'cause the tip gets mighty hot!
About practice steel, that's fine and you can buy strap steel at any home supply store, but my thought would be to start with A2 tool steel. Even the precision ground, which saves a ton of elbow grease is pretty cheap. I've seen it 1/4 x 1.5" v 36" for like $60.00, on line. You just never know what will be your "masterpiece".
I started hollow grinding with 1/4" stock. I think that is better for beginners 'cause you have a lot to remove and therefor more time to learn how to grind and opportunity to make adjustments (corrections) to the final blade.
Jay