A:AnswerAn eero won't provide you more speed than the ISP is delivering you. It will help you get those speeds at range and make the most of the speeds with all of your devices.
A:AnswerYou will want to use either another Pro 6E or 6+ eero. Both of those are capable of 160 mhz bandwidth on the 5 ghz channels, mixing in an older eero will force the Pro 6E to go to 80 mhz on the 5ghz channels.
A:AnswerThe eero 6 is actually cheaper even the eero 6 pro is cheaper than the 6e pro. However is deoends on sales sometimes the best product goes on sale to encourage shoppers to upgrade, take advantage of a good deal when you see it.