This is the exact same iMac I have now (i7, AMD Radeon HD 6770M 512 MB and user upgraded ram, only to 16GB though). I assume you're talking about the 2011 model. If so it's a very good machine. If you don't get 16GB ram it's cheap to buy that. It was a real pain to put in the 16GB ram though. A design flaw in my opinion.
About 32GB ram. I'd get a 2nd opinion on that but I think you can put 32 in that. I don't see that being a wise move though. I think 16 should be enough.
Is this computer a good one? Yes very even today. Is it worth $750 vs a full priced new iMac? Tough decision. I am tempted to say yes. I paid about $1800 for mine with student discount back in 2011. That's Aussie dollars so in US dollars would prob be 1600 with no discount.
I do use photoshop, iMovie, a little logic pro etc etc on it. All just fine. Nothing like 4k or 1080 full movies in Final Cut Pro X though. I'd totally get a 2nd opinion but I think for the $750 I think it is a relatively good deal.