A quick word on first grinding wheels and learning grinding in general.
To learn how to grind and learn the characteristics of a grinder I would start with a 32 grit Aluminum Oxide Vitreous bond wheel in a hardness of I or J. Your arbour sizes and diameter should fit your grinder. It is easier to learn on a 1/2" wheel because it puts less pressure on the work than a 3/4" wheel, etc.
Dress your wheel often. Know that soft materials, including soft steel, will strip the grit from the wheel, and load the wheel easier than very hard tool steel, so the wear in much faster on soft steel. Use that wheel up! Then, after you have a lot of experience on 32 grit, try a 46 grit wheel and see how things change. Every grinder hand I know has a different preferred grit/composition they prefer. Most recommend I or J hardness though - I don't understand why, exactly but that seems to be a universal bit of advice.
At some point you will need a second arbour for a diamond wheel. Pretty soon after you get really going on projets, you will eventually need to grind carbide: a drill, insert or scraper blade. This takes a very different set of techniques and is well worth learning, but you will experience different challenges and successes grinding carbide bits...
Buy or make a good dressing block with a medium or larger diamond. Dressing your wheels can be done with a small diamond, but it is easier to do with a little larger one, 1/4 carat or 1/2 carat will work well.
Best of all just grind with one type until you can predict the result in a variety of materials: regrinding hardened parallels, etc.
Lastly, mount a wheel on your arbour, and balance it, then leave it until you retire it! you can use up a wheel very quickly if you do a lot of shuffling around... I figure it is just lost learning opportunity. I have 3 arbours at present, with only 2 of them occupied. I have 4 spare wheels, all in hardness J.