Multi Proxy server 4G on raspberry pi 3

I'm looking for someone to create a squid proxy server solution set up on a Raspberry pi 3. The machine is on my local WLAN and connected to several USB dongles with 4g connection. I would like the proxy to be accessed remotely through Proxy IP:Port and it has to be anonymous (should not be detected as proxy), reliable and easy to use. It must be done in a way that im able to access the proxy with my WLAN IP and the outgoing IP address will change depending on the port im connecting to. Example: [login to view URL] (this is my local IP) [login to view URL] -> this connection will use my ppp0 IP address [login to view URL] -> this connection will use my ppp1 IP address I'm pretty sure this must be done creating alternative routes with iproute2 and iptables. I already have this server working as a 4g proxy server using ppp0 as default route, but i want it to use multiple connections at once, depending on the ports i connect. There's a scheme atteched so you all can figure exactly what i want