Hello,
This is a massive undertaking! But, you do realize someone is already selling something like this, right? It follows a user wearing a tag bracelet, navigates around obstacles, avoids steps, etc.
Also locates itself using GPS and sends SMS in case it is lost or loses track of the owner!
Special apps need to be developed, carriage and steering mechanism, guidance, power management, etc. It will require a team of freelancers in order to get this done in even the time I have estimated, so the budget might seem high. Also, the hardware must be produced and tested under load conditions. Moving a 35kg load for two hours at up to 8km/hr (5MPH) takes a LOT of power, and the weight of the batteries alone will be impressive. Have you considered the current "panic" mode the airlines have about batteries? Chances are the battery pack will have to be removable and carried on board with the owner. At the least, the packs will have to be certified, and that runs about $5000 ~ $6000 per pack design from reputable manufacturers.
But, as I said, someone is already selling something, so there must be a solution to these issues. But they will likely suck up time and capital, which I expect you will try Kickstarter or something.
If you are still interested, I can submit a detailed proposal and updated milestones (there will be several) once we nail down some more details, including my hiring plan for the additional freelancers.
Best regards,
Stuart Borden.