Your questions are difficult to answer. The Buffalo River is a natural flow river largely dependent on rainfall. In any given day in any given April, the water level at Ponca could be too high, perfect, or too low, especially for loaded open boats. Most of the rapids on the upper Buffalo are above the Pruitt access. The most potentially challenging is probably Gray Rock Shoals, which is a little more than a quarter mile above Kyle’s Landing. Gray Rock has three relatively closely spaced ledges, and at healthy spring water levels these can kick up some sizable standing waves and at least one good sized hole, any of which can potentially souse an open canoe. At low water levels, this particular rapid can become quite technical with the best route for a loaded boat not at all apparent from the top of the rapid. At the usual water levels that Ponca to Pruitt is paddled at, the rapids are all Class I or II.
Below Pruitt the rapids become relatively mild but rootwads and strainers can still pose significant hazards. The National Park Service map of the Buffalo River is available on-line and shows roads and access points as well as river miles and a few major river features:
You can enlarge and pan the map for details.
There are some topo maps of the upper and middle Buffalo available on-line primarily geared towards hikers:
National Geographic sells some reasonable topo maps of the Western and Eastern Buffalo which might be worth having along:
I am unaware of any maps that actually show the location of specific rapids.
Your trip is certainly doable but it is impossible for anyone to predict your average daily mileage. This will depend greatly on water levels, how many hours a day you plan to paddle, which will depend on how efficiently you can break camp, load up and get going in the morning, how many stops you make, etc. It may also depend on weather conditions. Do you plan to paddle if it rains all day? Even if you do, thunderstorms or high winds could drive you off the water.