Hi. First, it does not sound like this application points to the use of two routers. Two (or more?) access points – maybe. Two routers – no. (Don’t confuse the concept of router and AP.) The SOHO is a superior product but is limited to a single AP – logical for it’s role in the product line and market. If the circumstances suggest more than a single AP we’d probably suggest the use of something like the Balance 20 and as many APs as needed [up to the limit of the controller’s capacity, of course]. The Balance series has a built-in AP controller which works well.
We’d never recommend the use of an “extender”-type device. Better to just engineer it right the first time. While there are optional antennas, as you suggest, We’d not plan to use them from the start unless there was a compelling need. You may be well-served to look up a Peplink Partner in your area to help with this project if you are unfamiliar with planning and executing such projects.
And, yes, one can run WPA-2 only on Peplink/Pepwave devices.