Lllaass is on the right track. You CAN assign different SSIDs to give the appearance of different Networks, or you can assign the same SSID to give the appearance of one Network with two bands available. I recommend you use the same SSID for both. Then your Mac will choose the band and modulation technique that gives the fastest throughput, after allowing for noise and interference.
A dual Band Router provides both 2.4GHz and 5GHz bands. In most Routers, these radios can operate independently. 802.11n and 802.11ac are advanced modulation techniques that use only the 5GHz band, while earlier versions may use either or both.
Multi-In Multi-Out (MIMO) is an additional high-end capability that can use two channels simultaneously in the same band for improved signal strength, directionality, or just raw speed increase. 802.11ac with MIMO is worth paying extra for, and will improve performance in almost every case. Even if your current devices can not use it today, new ones you buy most certainly will.
Competition and interference on the 2.4GHz band cause no end of grief, especially in crowded neighborhoods where several other Networks are visible. It does not make sense to buy a 2.4GHz-only Router today.
The newest Apple Routers are high end and high quality, and easy to configure, which helps justify their high price compared to "bargain" Routers. But there is no requirement to have an Apple Brand Router.