I need to replace my front suspension forks with hard forks (no suspension). My bike has disk brakes, a dynamo (that seems to attach to the wheel hub), and mud flaps. Are these sorts of things easily added to any non-suspension fork or do I need to find something specifically designed for these needs? If so, what should I look for?
The wheel should attach to the new fork with the current hub.
You just need to match the tube diameter and height.
You need to match the height for a bike designed for shock. Like look at a Salsa Vaya compared to Fargo. The Fargo comes with solid but can take a suspension.
You did not post the size of the wheel or fork but this is an example of fixed fork that replaces a suspension. OrgeFork
You need to match brakes. Often they will support more than 1 brake type. That Orge supports disc I think - most 29" most do.
And checked used. Most people go the other direction (solid to shock).
You also posted a question on mounting a rack. Look for fork with mounts for fender and rack. Why did you decide to not put a rack on the suspension?
As for if you are on a budget should you go ahead and put a rack on shock?
I would say yes use the shock and put the money into a nicer rack and/or nicer bags. A decent set of bags is $100. Put your lighter stuff up front. A mountain bike with shocks for a road touring is not ideal but that is where you are. As for a point of failure I would not worry about that unless you have an indication you shocks are failing. If you can find a used solid fork with rack mount for $40 and can install it yourself then I would do it. There is a Salsa Fargo fork on ebay right now that multiple attachment points. If it fits your bike it would be nice. I don't know how much of a budget you are on.