Rhett,
In response to your questions:
1) AMSOIL is readily available factory direct. You can buy retail or wholesale. Because we are such a small company, you will not find us in any of the major automotive parts stores. There a many independents out there who may handle it. It's much easier and less time consuming to order it direct than to run around town looking for it.
2) The drain interval is up to you. AMSOIL guarantees its motor oils to perform for one year or 25,000 miles, whichever comes first. Using an AMSOIL SDF oil filter, just change the filter and top off the crankcase at 6 months or 12,500 miles.
3) It's OK to switch from dino. We do recommend that you flush the engine with AMSOIL Engine Flush (part no. AEF) when you are ready to change oil. Synthetics have a detergent action that is inherent with their chemistry. By flushing the engine of any deposits and build-up, you eliminate the chance of clogging the filter prematurely.
4) The AMSOIL SDF filter is the best filter on the market today. It filters more finer particles and holds more junk in the filter than anyone else. We recommend using the SDF filter with our motor oils for optimum performance.
Thank you for your questions. If you would like some additional info, please e-mail me. We'll be happy to help you out any way we can.