To deter mold, keep indoor humidity low. If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity. Relative humidity can be measured with a moisture or humidity meter, a small, inexpensive ($10-$50) instrument available at many hardware stores.
If your smaller projects call for clear pine without any knots, you can save money by buying a lesser grade, then cutting out what you need from the clear areas between the knots. Also, when buying wood, remember that face grain is not critical for structural parts which won’t show. You can likewise save on lumber costs if you can use shorter or narrower boards, or if you only need one good side of lumber for your project.