Need to upgrade router from a Linksys DIR-655

I have around 14 current devices using wireless N single band.
2 are capable of N dual band

and yes I have awful wireless speed on my DIR-655 wireless

I want to add....

a Roku 4 (AC) (Stream 4k)
3 laptop adapters (AC)

I'm trying to understand all these new speeds AC numbers and tech like Xstream and MU-MIMO.. So confusing to someone coming from a draft N 150 router. I'm reading that some do not perform too well doing both N and AC.. Obviously I hang on to tech for a while, so...

Need to upgrade router from a Linksys DIR-655