Looking to the time frame and materials required, here's my current thinking.

April, 2016

Create ability to find charging station. I will use the Pololu IR Beacon Transceiver Pair and program the bot's Arduino to utilize the information received from the IR beacon. If this fails, my backup system will be to use the Pixy camera (I've done this on another project, but power consumption, lighting and expense put it in the number two position).

May, 2016

Build the charging station and pickup points for the bot. I'm thinking rollers and rails from an O gauge train may work for this.

June, 2016

Add people sensing and "excited to see you" routines. A PIR sensor will be used for human (or animal) detection. This is more tricky than I first thought, since the bot must be still for the "motion detector" to detect motion that is not caused by the bot.

July, 2016

Add stair detection. Some sort of IR detectors will be used for this.

August, 2016

Build a people friendly body, including eyes with servo controlled eyelids.

September, 2016

Build Taco, the people friendly "shell" for the charging station. Taco will have servo controlled eyes that "blink" when Mato passes by.