Building the hardware for the Flea is only half the challenge. It will also need to have some appropriate software written for it once I have decided on a payload.
To make my job easier, TI have released an updated Reference Design - http://www.ti.com/tool/tida-00488 - Energy Harvesting Ambient Light and Environment Sensor Node for Sub-1GHz Networks Reference Design.
This design uses a CC1310 MCU/Radio, in conjunction with a couple of I2C sensors. On the power side, it uses a TI BQ25505 energy harvesting IC to convert the power from 2 small solar cells (coincidentally, the same type as I have used for the Flea!!) It uses capacitors for storage, and a CR2032 coin cell for when there is not enough solar power.
Thinking about it, the BQ25505 is probably a better choice for the EPS, rather than the LTC3105. But as my design was based on a previous project, I just used that.