Need advice on new AC or N router using ATT DSL modem

[liblady]

Hello, I need to upgrade routers and have read too much now I'm just perplexed! Currently have ATT 411N router. Have medium size one-story home with outdoor wi-fi usage. Have PC desktop wired as well as few wireless printer, PC laptops (Win 8.1), iphones, ipads, Apple TV, Dish, smart TVs, etc. Now experiencing lag & dropped service. Main questions regarding reviews read - Can I use my 411n as modem alongside new router? AC or N? What is Bridge and do I need this? Should I purchase a cheaper router w/range ext. or go with a big dog expensive one? Any input, advice is much appreciated for this middle-aged non-techie?