Buy the H-D shop manual for your bike. This will tell you everything there is to know about your bike including routine maintenance. Engine oil change is every 5,000 miles based on using regular petroleum (dino) based oil. Synthetic will allow you to go further, but I still change at 5,000 or less even though I use Amsoil 20-50 MCV. Transmission lubricant is every 20,000 miles, again based on conventional lube like H-D Formula+. Synthetics are optional, but better. I use Redline Shock Proof Heavy synthetic gear oil and change once a year regardless of miles. As for the primary, every 10,000 miles. For me that means once a year and I stick with Formula+ since synthetics are overkill for the primary. A lot of riders change more often than that with synthetic lubes, and that's fine. There is no such thing as treating your bike too good. I just don't believe that there is any appreciable advantage to it.
Whatever you decide to use and how often is strictly up to you, but the baseline is the shop manual. Follow this and you can't go wrong, but if going a step or two further gives you satisfaction, go ahead. The cost of any lubricant is chump change when it comes to the maintenance of a Harley, but it pays dividends in the long run.

 

I have been doing Amsoil in everything for last year, did change at 10K, no problems, much better MPG, and oil looked fine at change over.