Do you think that a 70D is a good choice as a first Canon DSLR? What are its main advantages compared to a 700D?
It is a great choice. The 700D may be even a better choice, and I will argue this point.
I start with a disadvantage of the 70D: the AF system can be quite daunting to use properly and if used in automatic point selection mode it does not really offer an advantage over the 9 point system used on the 700D.
My first DSLR was a rebel (the 350D) and I chose it intentionally knowing that in case I "failed" the loss of investment was smaller than if I started with a more expensive camera. Starting with some constraint will allow you to save money and spend more for better tech down the road when you are more experienced and want to update your gear. This is a point for the 700D.
OTOH if video and live view AF are important factors, then the 70D is the camera to go. Ergonomy is better as well.