1. Around April/May firms will start sending out advertising/information packages to schools, and there will also be the ICAA's function where you meet alot of people from the firms and can ask questions/etc... Applications are usually due mid-June (note: this can vary so keep checking the various firm websites) and as mentioned above, are usually done online.
2. It's possible but not recommended as even with just 2 subjects; if you want to maintain your focus on work, it's extremely difficult to excel in work and study. I'd also recommend you take the first semester slow just so you can settle in, and if you feel comfortable, maybe in your second semester you consider an extra subject.