Just my 2 cents worth here, but you have to decide on a management plan that you can maintain over the long haul, as unfortunately, diabetes is going to be a part of your life from here on out. I'll be coming up on my 5 year D-anniv. in August, and the way I manage things now is a bit different from the way I started out. It's a journey, find what works with you and give it your 100%.
Sounds like you've made some great changes, and have that A1C to show for it!
I've went for a few months eating the Bernstein plan, i've eaten 50 or less carbs a day, I've fell off the wagon for awhile and eaten badly, and finally ended up where I am now, eating approx. 100 carbs or less/day. This works for me w/o making me feel deprived.
As for worry, there are days I worry, but worry does nothing constructive, so I try to do this as little as possible. I live my life with diabetes, tweaking it as necessary and as tolerated.
My doc suggested that I get off metformin when my A1C was at 5.2. I stopped it for a few weeks, noticing that my blood sugars did start to increase within the first couple of weeks. Even eating lower carb, I didn't see the same blood sugars as I did with the metformin, so I resumed it and have been on it ever since.
If you wish to try things off the metformin, why now, as you can always resume it should you need to. Congrats to you on all of your successes thus far.