Although the annual return of 8% based on the last 3 months may not seem great, remember that these 3 months have very much been the learning-and-experimenting phase. With refinement, it's possible that this return could/will increase.
1) Why AMZN? Due to the high price of the underlying? Last Mon was a good time to do an AMZN strangle (as you realised) but that was due to the big fall in the market and increased IV. This week, I wouldn't recommend AMZN as they report earnings on Thur. From next week onwards, you may find the premiums on the 5D strangle aren't quite what you may want to be.
2) I'd be interested to hear about your SPX iron flies - I tried many, many times to make these work, but I consistently lost money. I found the IV on SPX to be too low compared to the actual movement.
Calendar on SPX - be careful with these - the profit tent is quite narrow and the index can easily shoot above or below your breakevens in a day or two. Gamma risk is very real with calendars, and I'd only recommend if the vol of the shorts are way higher than that of the longs. That usually happens when there's a big down day. But no free lunch - a big down day is often followed by a biggish move (in either direction) the next day.
Good luck.