Hey guys! I'm looking for a solution to a couple features i need in my WAN network. Here's what I'd like: 
1] Master router (RT-N12E) inside, plugged into LAN.  
2] Outdoor extender for the Guest network with a signal radius of about 200m = ~500ft (master will be 20m away). 
3] Guest network/slave must have captive portal, no registration, just a popup and confirmation. This captive portal must allow an iframe with an external webpage. Captive portal ideally setup on external site. 
4] If the master WLAN is unavailable, fall back to a TPLink E5250 pocket wifi with HSDPA.
5] Most importantly - Guest network/slave needs to have URL redirection. Not IP filtering/firewall, but real redirects. So eg. google.com redir to google.com/images. I would prefer if these rules could come from an external server/php script so that I can edit them from anywhere without touching the router software. I have hosting servers for the external stuff and PHP/HTML knowledge to set the external stuff up.

I have been looking at the RB912UAG-2HPnD or 5HPnD (not sure which to choose). But I like that I can upgrade to PCIEm in the future and not have to use the TPLink.
Here's a little mock-up of what the network should look like.



Is this doable? Thanks in advance for any advice!

Any ideas?

I've found answers to most of my questions, now I'm just not sure whether to buy the 2.4 or 5Ghz version.
Will 5Ghz be able to penetrate into a nearby house if placed 20 or so meters away outside?

It's impossible to answer
Everything depends on the materials making up the building

Its made of porous cement blocks. No metals.

So it may work, but you have to try to be sure

Maybe it will work after the first wall, what about the second wall or the other room? Do not forget, WiFi is a TWO way protocol. Not only your MIkrotik device should "penetrate" the walls, but your user device (Apple, Samsung, exotic WiFi radio) should be able to "scream" back to the Mikrotik. And he should hear the device at a 10% rate from the download speed.

Since your users have phones etc... and they have poor power radio, your limit will maybe not the Mikrotik, but the user.

So I ended up getting the BaseBox 2.
Now after some fiddling around, I'm not exactly sure how to set it up. I'm basically following http://wiki.mikrotik.com/wiki/WDS_repeater_example but since the main router is an Asus RT-n12e, I can't use WDS slave. I'm using static pseudobridge for wlan1.

Can anyone give any pointers how this should approximately be set up in Winbox?
This is what I have set on the Asus side: