Captive Portal and initial setup!

Ok, I have no idea where to begin, my ultimate goal was that when a user enters my “Guest Wi-Fi” SSID, a welcome webpage appears to him before he/she browses the net. I’ve looked around a lot and found RouterOS.
Now I installed RouterOS on a virtual machine and now I have no idea what to do next! sooooo many options!!! O_O…
Anyways let me first explain my layout and hope I don’t need to re-arrange…

{INTERNET} — {Linksys E4200v2 Router} — (8 port Switch) — (7 Access Points connect to the switch) — around 2-3 devices connect to each AP either by wire or wireless including my PC which is hosting RouterOS in a VM.

Only the main router has a guest SSID broadcasting since it is the one in the guests room, so can I let people who connect to this SSID be directed to my webpage as soon as they open a web browser program?