I would still got upto a 150g at the least if ya plan on keeping all the Oscars and SD's. Those Oscars will get big, atleast 16-18in big. That and they take HUGE dumps, mine used to leave almost small dog/cat sized turds in the tank even at only 8in so just imagine what it'll be like when fully grown. That and then add in the extra bioload from all the SD's. With a 100g I would imagine almost bidaily-daily waterchanges just to keep the tank clean. Even with a 150g like I mentioned would still be a twice a week waterchanges just to keep the water clean.I have roughly 100 g tank for the Oscars and dollars... I know a little small. But I used to have a smaller one for two and they paired fine.
About 80 g for the cichlids.
Not trying to sound mean here, just trying to help out as much as I can.