Angels ...

Absolutley!

Goldfish are coldwater and cannot be kept with angels and goldfish grow medium,biggest i seen was 20 cm.

yup and they make alot of waste too,they also dig the gravel.

Angels need plants,they feel safer that way,the goldfish will wreck the place if there is plants,since they eat anything non stop.

In general, the fish you are keeping, all get to large for a 20 gallon. The goldfish, whether it be comets or koi, will get to large. In addition, they produce tons of waste. The angels will also get too large. Personally, I would not keep them in anything less than a 55 gallon. However, a 20 gallon is fine if you are seperating them in order to try and breed them.

But no, they will not fight.