I really enjoyed my time abroad in Seville and especially at UPO! My host mother was wonderful and Seville is a fantastic place to live. Everything is within walking distance or easily accessible by the metro, and it's very safe (even at night). There are a couple of things I wish I had known before coming, though - international students typically don't take classes with Spanish students and are actually on a different semester schedule, so although there is the opportunity for language exchange partners, it was a lot harder to actually be immersed in Spanish than I expected. Additionally, the add/drop dates for classes are very short, only 1-2 days of class, so it's hard to switch Spanish classes if you end up in the wrong level. That being said, all of my professors were wonderful and we also had Fridays off every week, which meant we were able to travel much more easily!
Adelante did give us the wrong semester dates during the summer, which meant I had to switch my flights after coming to Spain, but they did send me a refund for those additional costs. However, they also recommended that students not apply for visas after the semester dates had been extended, which I was uncomfortable with given that we stayed past the 90 days allowed for tourists. I ended up getting a student visa regardless and am glad that I did (and would also recommend future students to do so)! It's also worth noting that a couple of things advertised on Adelante's website or in the orientation packet didn't end up happening, like the first-week meeting with the on-site director.
A couple of other things to note are that the 2 meals provided are usually either breakfast and lunch or breakfast and dinner, so I would definitely recommend bringing a container or two for lunch and some packable utensils. Meals at the cafeterias are around $5, so although they're decently cheap on occasion, they're less affordable on a daily basis. Seville also does get cold, so I would recommend packing warmer clothes! It stays a lot warmer than most of the US, but because a lot of buildings and home stays don't have much indoor heating, it can still be really cold indoors. Also, everything outdoors is built to channel wind so it stays cool enough during the summer - which is great, but means the fall/winter can be freezing if you're outside!