Start with some soft brushes to begin cleaning it. ( Makeup Brushes that can be found in sets and a variety of sizes in the drugstore makeup section are good) I made a cleaning hood out of a cardboard box with a square hole cut in the back to press fit a furnace filter into. Then a box fan turned to draw air through the filter behind that, as close snug up against the filter as as you can put it. Collects most of the dust. Blowing air on it, not so good unless done very gently and judiciously.
Then find plans for a ship or ship model that most closely approximates your model in time , history, purpose and design as a guide to re-rigging and re- assembling yours. Take pictures against a white background and, if you can, make one to one scale drawings of how she looks before disassembling her. ( A good pair of dividers is necessary). Try to stay as faithful to the original as is practicable. The original finish looks pretty good under all that dust. And remember, they're only original once. Even though the original blocks look a little clunky and out of scale, you might want to consider reusing them if only to maintain the folk art charm of the model.
Pete,
Feel free to contact me through the mail option on the lower right of the SOS banner, just below the ship. I've done a lot of these. Maybe I can put you in touch with Peter Sweetser in Chestertown MD. He's a professional. And of course there is the book "Caring for Ship Models" by Rob Napier, Sea Watch books
Above all be patient with the model and yourself, use your imagination and have fun. It's a voyage of discovery. After awhile you will begin to develop a feeling of intimacy with the original modeler. It becomes quite a spiritual sensation after awhile, the connection to the past and a long deceased ancestor.