I'm looking at the Generac GP17500E portable generator for my house. The large 50A receptacle only delivers 12,000 watts. Generac says you have to get the other 5500 watts from the other receptacles.

My question is how do I get these other 5500 watts into my main load center? Do I run 2 manual transfer switches, 1 with the 50A and the other with one of the 30A outlet? If so, is there any special wiring needed when using 2 switches, to keep them isolated from each other?

I must be missing something, it seems this would be a lot of additional material & time to install?

50 amps at 240V is a lot of power... how much do you need?

An issue here is that this generator has been designed with receptacles for output power.
I cannot recommend use of equipment in any way other than intended by the manufacturer.

It sounds like you should consider a larger genset that you can connect directly to a transfer switch and your house panel... (I assume this would be a home system)

Do you really need more than 12000 watts? What are you needing to run?
Why such a huge portable generator? That thing is a monster!
Why didn't you just go for a whole house standby unit?

IMO more than a 12kW portable unit is overkill and not worth the effort.

And no, you definitely cannot run two transfer switches to the same panel. You'd need two switches, one feeding the main panel and the other feeding a sub-panel.
That is also a lot of added cost and work.