I consider to buy Dual Band RouterBoard, but I have a few questions, maybe someone can help me.
1. Can I start two wireless network at once (hap ac or hap ac lite), one 5 GHz and one 2.4 GHz for my old devices?
2. Is the 5GHz signal strong as 2,4 GHz signal?
3. Can I reach higher speed of transmission in 5GHz band?
4. What type wireless adaptor have to buy for my old Laptop Lenovo B570e? 
5. Can I change wireless adaptors of my phone Sony Xperia M2?
Hope someone can help me
Thank You

1. Yes, you can use different SSIDs for 2.4 and 5 GHz. You could also use one for both bands. The devices will figure it out.
2. Unfortunately no, 5 GHz has less range than 2.4 GHz.
3. Yes, there's the new 802.11ac standard which operates on 5 GHz exclusively.
5. Probably not, most smartphones aren't modular.

Thank you , Imns! About fourth questions, I found adaptor for my laptop. Thank you again