Network Setup - how to deploy pfSense

[bfts]

Dear Geeks  ;D

I'd like your advice on how to properly set up my networks and where & how to deploy pfSense.

I'm setting up the network for backpacker hostels in South America, generally internet around here is still pretty slow (at least where I am: Bolivia & Peru): max 4Mbit/s, so all setups are MultiWAN, generally connections are ADSL with no access to the ADSL Modem.
(The techs that install the modems usually don't bring their own laptop though, so a key logger on my own computer can give me the modem passwords in some cases).
On the LAN side we have 3 networks, the Office(LAN1), Internet Cafe Style client PCs (LAN2) and a free WiFi (LAN3).

I wonder what you think is the best way to deploy pfSense in this setup?

Currently I am running an old Pentium D box for MultiWAN (via VLAN), the 3 LANs too are connected via VLAN.

I would like to properly block LAN2 & LAN3 from accessing LAN1, traffic shape all traffic, keep a minimum bandwidth for LAN3 always available, block certain websites (Facebook) for certain clients on LAN1, block/throttle torrents (or any unusual/unspecific traffic) on LAN3 and maybe even be able to VPN into LAN1 from the outside….

It looks like traffic shaping with minimum bandwidth is difficult with MultiWAN, so I was considering either a 2nd pfSense box or some cheap TP-Link (?) multiWAN solution.

What would your suggested setup be to achieve the mentioned?
Should I try to get access to the modems? Should I try to port forward everything to the pfSense box (DMZ)?
How would you set up the LANs? And the WiFi?

Thanks