My experienced-based opinion on this topic's title:
In general, yes.
Where a combo is better:
When it's a non-tech-savvy customer, I'd recommend a rental/leased combo modem from SPECTRUM. The Ubee and Technicolor ones we have currently in stock can do the 20+20+20+20MHz channel bonding on the 5.0GHz WiFi, which is nice for those 802.11ac devices you may have (noticably faster than 802.11n).
It no longer costs $10/mo extra to rent those (under TWC it did).
Where customer owned modem and seperate WiFi router is better:
Power users, gamers, and tech-savvy people.
If you're going to do your own WiFi router, why not do your own customer owned modem too? The features and signal range of stand-alone WiFi access points or routers you can own/buy are generally better than any gateway modem (which is the proper name for a modem-router combo, a "gateway modem")
It's not $10 less to own your own modem under SPP, same price for rental or owned modem.
Under the Wireless page of 192.168.0.1 :
the 802.11 Band is currently set to "2.4GHz". Should I set it to 5.0GHz ?
You most likely have some devices that are only 2.4GHz capable, like older laptops or wireless printers, so both 2.4GHz and 5GHz should be active. If all of your devices are 5GHz capable and are fairly close to the router you can get by with only 5GHz active but then you're giving up some extended range.