So a 200 gallon is best then
Imo, a 200 gallon would be too small with the other stock (tinfoil barbs, silver dollars and angels) that you mentioned.... unless you are prepared to do 75% water changes every 3 days.
If you are, it's feasible. If not, your water quality will suffer due to nitrate buildup, fish appetite and immunity will decline, and you'll be dealing with multiple problems.
If a larger tank would allow you to do larger water changes (more water but less frequently), then a larger tank would be "best." Otherwise, what might be better is to skip tinfoil barbs, angels and silver dollars) and maybe opt for something like a couple colorful and peaceful variety of tetras.
Alternatively, as an example, just angels or just silver dollars with the fire eel. Alternatively develop a lot of plants for the tank (e.g., pothos), to minimize the nitrates.
Lots of choices and the surface isn't scratched. But a 200 gallon with that other stock and infrequent WC will not be best, imo, in a tank that small.
And this assumes the fire eel only gets to 30", which is by no means it's limit in aquariums.