Way back, when I purchased my first KMG, I got a 1 1/2HP motor. As I gained more experience, I went to a 2HP, and after that motor went out, I did two things..... upgraded to a 3HP motor, and changed my KMG to a direct drive. I passed on the direct drive conversion information to Rob, as I feel it totally changes the personality of the machine (for the better). Now I look at it this way....
You can only get some much out of a smaller motor, and once you reach that limit, you're either stuck there, or you must upgrade (spend more money) to get any more. If you have a larger motor to begin with, you have room to "grow" into that motor.
It's really going to depend on YOU....what you want, and of course your pocketbook. I know plenty of makers who have worked their entire careers with 1 and/or 1 1/2hp motors on their grinders, and have never been disappointed.
Personally, for me, and the way I grind, the most important attachments are a flat platen, a 8-10" contact wheel, and a 3/4" small wheel. Grinders and attachments are one of those things that most makers tend to modify to best suit their personal needs/wants. When I'm "in the groove" grinding, I personally hate to take the time to unbolt an attachment, and bolt another in place. To that end I designed my own flat platen, and attachment system for the KMG tooling arm...well, more like took the idea from my old Square Wheel grinder..... my tooling arm(s) have a 3/4" friction fit hole, and all my attachments have a 3/4" pin. To change attachments I leave the tooling arm in place, take 1/2 turn on a "handle bolt", insert another attachment, tighten the "handle bolt" a 1/2 turn, tighten the belt and keep going.
http://www.caffreyknives.net/grinder_platen.html
Having every attachment is nice, but you'll quickly find you only use a few. When Rob Frink first started making the rotary platen, I was a "tester" for him. While the rotary platen has many applications, I find that mine hangs on a peg more then it ever gets used. Convex grinding and radius grinding is where it really shines, but those are also things you can do on a slack belt. The rub with attachments and starting out is that unless you have a number of attachments, you'll never know which ones are most important/most used for YOU. Once I figured out the ones I used the majority of time, I ended up selling off all the others.
Motor size is going to be strictly up you you, but for me, 3hp seems to be the "sweet spot". IMO, the most "bang for the buck" you can get with any grinder is having it setup with a VFD (Variable Frequency Drive). It's one of those things that you never would know you need, until you have it, and experience it's benefits, then you'll wonder how you ever did without it.
Most makers tend to adapt grinders and attachments to the types of knives they build, and the methods they use while grinding. In other words, what works for the individual, and what the individual likes. The tough part is finding those things. In the end, you either have to buy ALL the attachments, and find out which ones suit you best, or you buy some here and there (when you can afford to), and some are "keepers" and others either hang on a peg forever, or get sold off when you find you don't use them.
