OK, Colin, you've convinced me that you've chosen the right design. Another saying we might throw in here is "Go small, Go simple, Go now" (Lin Pardey). In an ideal world, the singlehanded cruiser has the luxury of a 29ft, 4 ton boat (or in the case of Hobbits like Annie, a 26ft, 3 ton boat). But we don't live in an ideal world, and we have to do the best we can with what we've got. Annie's right, the Pioneer will make 1000 mile passages easily enough. A 3000 mile passage across the Atlantic is in a different league, though, and needs building up to, with several years of less demanding passages.
Enough with the philosophy. What needs changing on the Pioneer 23? Not much. Mainly a question of laying out the accommodation to suit a singlehander living aboard, rather than a young family of four weekending aboard.
I'd put a full bulkhead 7ft forward of the companionway bulkhead. Forward of this would be the heads, hanging space for coats, and stowage for an inflatable tender, warps and fenders. Immediately aft of the bulkhead, 2ft of length on both sides would be devoted to the galley, cooker on one side and sink on the other. Then two settee berths 6ft6in long, with 1ft 6in in a "trotter box" under the cockpit. Under the after halves of the settees are battery, tools and spares. Under the forward halves is food stowage. Outboard of the settees is clothes stowage. Under the cockpit, in place of the engine, is water stowage, 6 x 10 litres.
The only thing that needs mentioning to Paul Fisher is that full main bulkhead. The rest can be done on an ad hoc basis.
Without seeing the plans, I can't comment on the doghouse that is only vaguely sketched in. Certainly the form of the companionway needs to be different for serious cruising from that for weekending in good weather, but that part of the build is a long way down the road.