You are making this too complex and you actually increase you chance of a security exposure since there are many more places you can make a mistake.
The firewall and the router perform the same function....at least in a home environment. You generally do nto even need a firewall unless your plan is to put a server on the internet. A simple router by default blocks all incoming traffic from unkown ip addresses. This is why you have to put in port forwarding rules etc.
A load balancer is a complete waste of time unless your goal is purely for redundancy and even then it can be questionable. .
How does the device know the connection went down. In most cases the modem will always provide ethernet even when the connection is down. The load balancer would have to have some method of seeing sending traffic to test both connections. And again what happens if it is losing 50% of the data is that bad enough to switch. Commercial implementation use routing protocols to solve this issue. For home users it is generally easier for the person to notice the internet has issues and manually switch over. You would hope this does not happen often.
There is no realistic method of combining 2 home internet connection to provide more bandwidth on a single session. The IP addresses are different so machine on the internet assume they are different users. This is a fundamental restriction that you can not get around. Now you could try to send some sessions one connection and some on others but this tends to have large issues. The example I give is a game company since many people on this forum know about this. Say you use 1 connection to log into the authentication server. You then use the second connection to log into the world server. You now have connected with 2 different IP addresses. The game company will detect this has hacking. How can any load balancer know all the game companies and make sure this does not happen. This is far more than game companies, think about web sites that use different servers for their credit card processing.
Thanks very much for the info. The firewall was for your indicated potential. In the future I was interested in expanding to include a web and mail server to carry my partner and I's websites/email.
I'm keen to hear any more info you have regarding the IP as I thought this was entirely possible and half the purpose of this device (and/or software I've seen as well) to mimic your network traffic as to all appear from 1 IP.
Ok as I was typing that and thinking, yes, I see where you're coming from. In terms of your gaming example I can see the issue.
With regards to other items I assume it would still work for things like P2P file transfer and I suspect downloads if utilising a download manager?
Regarding redundancy, my assumption was that if one went down then internet would at least still be available through the other. I'm not sure how manual switching would be required?
Perhaps I just don't have a great enough understanding yet.