Designing a 2S Li-ion charger with 5V 2A input
Assuming I can easily boost the voltage up what should I consider in
  the actual charging circuit


You should consider offers from Texas Instruments, Maxim Integrated, or Analog Devices, and few other companies, who offer a lineup of chargers (battery management ICs), and use their design tools to select the best match for your project. They would have many "useful example circuits".

The assumption about "easily boost the voltage" is most likely wrong.