Is your phone on most or all of the time? Do you use a GPS while on the road? Will you be camping where being able to plug in is rare?

If you said yes to any of the above you might benefit from a dynohub. If not, you can probably live fine without it.

The cost of a good hub and spokes is not insignificant, you might consider getting a new rim too so you would lace up a complete new wheel, as a rim is almost cheap in comparison. I notice you are in Madison WI. I used to buy spokes at Yellow Jersey but they moved from their State St location, I am not sure where they are now. But they used to have the best price in Madison on spokes if you buy local.

I am not sure why you would need two hubs. You could get one. If you think you need a second, do that later.

My dynohub (SP Dynamo, PV-8) is on a 26 inch wheel. My last tour I used my 700c touring bike that does not have a dynohub. I usually try to carry a week supply of batteries for my GPS which is always on while I am moving, I use AA rechargeables for the GPS. There were times on my last tour that I was running low on power. I described my electrical experience on that tour in more detail here:
http://www.bikeforums.net/touring/98...l#post17394750