If you're on a serious time constraint, you could get a good quality USB battery bank. They handle charge management and balancing, and they output 5v so you would only need 3 ti regs. You'd need to make sure it can output enough current though, as some banks are capped in that regard. The drawback would be a loss in efficiency since the board would be stepping up cells in parallel from 3.7v to 5v, and step ups are less efficient than regulators. This is how I did it in my portable, and I can link you to the bank I used if you're considering this.