For events, you're definitely gonna want that that 70-200. There are plenty of times you can't be right up in the action for one reason or another, and being able to get the shot from a distance in priceless. Needless to say, a good tripod is a faithful companion for that and many other reasons.
The Sigma Art 18-35mm lens would make a great companion to the aps-c sensor in your 70D, it's actually made to accommodate that size sensor. It would give you an effective 28.8-56mm range, which should be plenty wide, and would compliment your 50mm (which on the 70D is effectively an 80mm lens) quite well. It's also pretty fast at 1.8, which would help you out in the low light department. And it's only $800 :)
Is the sensor in the URSA the same as in the production 4k?
The micro studio actually looks pretty cool, their 4k sensor in a tiny, cheap package? It's a shame that you'd need to add on an external recorder for at least $2k to actually get 4k out of it, and then you're at the price of the Ursa Mini. I guess it will at least have really nice 1080p footage coming from that sensor with the down convert.