Dual WAN and destination website routing
I am looking for some help in order to make a choice and upgrade my current network stack. In our small office, we have a huge internet issue (ADSL connection really far from the ISP cabinet, 1mb DL, less than 300kb UL when we are lucky and the wind blows in the correct direction while the stars align), and as for the moment our ISP is not planning to improve the connectivity in the neighborhood, we are looking for an alternative, in our case the only that seems could work is using a 4G modem.
The connection is pretty good (20mbit DL/4 mbit UL), however there is a big limitation in data (80GB / month).
As we are not planning (obviously) to remove the other cabled internet connection, I was looking for a dual wan solution, and pfsense could fit the bill.
I was thinking that, in order to avoid to go over quota with the 4G connection, it would be great if the router could do some "smart" routing, reserving the speedy connection for office related traffic (e.g. mails, file transfers, web browsing, etc), while routing "non-office" stuff to the slower connection (e.g. browsing addresses like facebook, youtube, etc. In other words don't care if the upload of photos on facebook or the coffee break youtube video buffers forever :D)
Note that I am not thinking about filtering based on content (don't even know if that is possible), I was more thinking about something like "let traffic to destinations with facebook in the address go towards this secondary route", or "let any traffic coming from this specific office PC go through the fast route", or again "let traffic to and from standard POP3/IMAP ports go through the fast link".
Would it be possible to implement a behaviour like this one? Or is it too complex?