a) as *A Gold you have access to JJ lounges. There are nice ones at GRU (International) and GIG, but there are no lounges at IGU as far as I remember. It's a tiny airport so it really isn't too important.
b) Connections usually work out well with JJ although flights are not the most prompt in the world they do usually accomodate connecting passengers pretty well. There's a new law providing for compensation for delays above 4 hours and that's helped some.
c) Remember Brazil domestic flights have carryon limited to 5kg and they're forced to comply. Do not forget that!