That interlock kit sounded good on paper but it's the klugiest looking
thing installed. I'm thinking to that I'd like to have a sub panel
and have that switched as well so I'm going with the old fashioned
transfer switch.

Once you install the interlock kit anything that is supplied from that
panel, including sub panels, can be supplied by the generator
connection. The only limitation is the capacity of the generator set
itself.
--
Tom H