I'm taking 20 credit-hours, my roommate is taking 25 this semester. 25 credit hours is hard, at least at my college along with the very demanding athletic team for which he has daily practice. My 20 amounts to 6 courses, 4 on one day 2 the next day. This is considered an average load at my school for freshmen. I also haven't picked a major yet, which will increase my mandatory courseload to graduate, and increase my credit hours, but i will also have knocked out the core courses that fill up my schedule before declaring a major, so I hope to stay balanced around 23 per semester maximum for the rest of my undergrad. I didn't even know about ECTS beforehand so I can't offer an opinion on that conversion ratio, but if 51 ECTS is really around 30 credit-hours, that is beyond fucked and I hope for the sake of your sanity that it is not the case.