Good luck with yer 'mater's. We grew Brandywines of various colors over the last couple of years, and found that they grow into huge plants, but are pretty shy bearers. We've grown pink, yellow and blacks, to us, the yelllow's tasted the best.
We've also grow Cherokee Purple over the last three years, and they've been hit or miss. When they're good, they're very good fruit.
Don't know about SS100, I assume it's a cherry variety? We've had very good luck with Chocolate Cherry, very tasty, and productive.
The 5-1-1 prob is good for getting a lot of green growth at first, but may not help with fruiting. You will prob eventually need a fert with more P and K as the plant gets bigger to help get those tom's started and growing.