With each WiFi radio, you will be sharing air time on the channel. Most routers will handle 25 clients with no problem. Many people in the past have even gotten 50 clients running on an old WRT54GL.
To minimize performance impact of many users, you could add more radios, for example, a TP-link C3200 would handle more clients than the R7000 http://www.amazon.com/TP-LINK-Tri-Band-Wireless-Archer-C3200/dp/B00YY3XSSA/ref=sr_1_1?ie=UTF8&qid=1457674039&sr=8-1&keywords=tp-link+c3200
Depending on your connection speed, it would not really matter unless you have a WAN connection in the 400+Mbps range where the overhead from airtime sharing starts to cause issues (assuming all clients are trying to saturate the connection at the same time.
For the easiest setup, the R7000 is very good, as it has a very even upload and download priority (it tries to give everything an equal amount of throughput).
Since it does not offer band steering, it will be difficult to force a balance of clients on the 2.4GHz and 5GHz band, but with 25 users, it will not have any issues with that work load.
Here is a test of my R7000 and how it does a good job in sharing the throughput.
Furthermore, it has some really good QOS presets which does a generally good job at keeping ping times low while the network is being saturated, while also identifying bulk traffic and keeping it in a low priority pool.
If you can get a good deal on the R7000, then it may be worth a try, especially if you have a decent return policy.
For many consumer level routers, they tend to have the same WiFi chipsets and front end components as many enterprise level APs, the main difference is that the enterprise stuff goes through more of a validation process to handle an enterprise workload.
both my phone and my laptop have wireless AC adapters, and they connect to various wireless N and G(eww) routers throughout the day, so I doubt you'd have any issue.
ac should be able to do, for best performance with wireless, it always good to do a wireless survey so that you can choose a channel with the least inteference, if you have an android device, I suggest wifi analyzer