Rio to Ilha Grande
You can simply take a bus from the rodoviaria (Novo Rio) to the jumping off point for the ferry to Abrao, either Conceicao de Jacarei or Angra dos Reis.
Coordinate the bus schedule with the ferry schedule.
Bus and ferry schedule here:
http://www.ilhagrande.com.br/como-chegar/
There are also transfer services that pick up at hotels. You can read reviews from people who were satisfied and those whose experience is that it made the journey much longer than the bus, contrary to their expectations.
Ilha Grande to Foz do Iguacu
You should fly, either from Rio (reversing the route above) or from São Paulo (cheaper, shorter, more frequent flights; a bit longer to get there by bus from Angra than returning to Rio.), perhaps adding a visit to Paraty on the way.
You may want to think about flying to Foz on your arrival to Rio or São Paulo, instead of later in the trip.