Good questions.
1) I don't need a phone and I agree getting a new phone isn't very economical. However, we don't own a computer and do all of our internet use exclusively through smart phones (our current phones are 3 years old at this point and slowing down quite a bit plus they are CDMA). The nexus line of devices are cheap and have good build quality. The other option would be to get a used phone on ebay, but it wouldn't save me that much money.
2) Yes the 100 min talk, unlimited text and data plan. I rarely talk on the phone. Long calls are usually done in video hangouts. It's not unusual for us to go without using any talk minutes. I'm a data hog, use approx. 4+ gigs per month. The t-mobile $30 plan is the cheapest on the market I think with 4g data speeds.
If you know of any other plans that might be good please let me know. I'm open to other suggestions!